For context, I don't study philosophy; however, I often have philosophical discussions with fellow university students. One of the topics that came up recently was:

Disregarding any moral obligation to obey the law, how mature must someone be so that having sex with them isn't unethical?

If someone over 18 (in USA) isn't mature either physically or mentally, then I would say that it is unethical to have sex with them; the law doesn't make it ok to have sex with them. (I would argue the converse is true as well, but there is no need to go there.)

My question is this: how mature must someone be so that it is not unethical to have sex with them? I am not looking for an age, or a law; I am looking for something more objective.


3 Answers 3


There are many factors to take into account, one of the most important of which is the idea of informed consent. If someone is unable to make an informed judgement about the consequences of their actions- wether through immaturity or not- it is considered unethical to take advantage of their vulnerability to being misled. This principle applies to most aspects of life, not just to questions of relationships.

  • (+1) thank you for your answer Commented Dec 31, 2023 at 10:19
  • Importantly, this "informed consent" ability should probably depend on both participants, not just the person who gives consent. Many countries have laws that are much more tolerant of sex between two underage participants than of sex between one underage and one older. Relatedly, one of the reasons why incest is considered so wrong is because the older family member has a huge ascendancy on the younger family member, which affects the ability of the younger family member to give consent. In other words, incest can be seen as an "abuse of trust" committed by the older family member.
    – Stef
    Commented Dec 31, 2023 at 10:56

People misunderstand the age of consent. In the UK less than 5% of rapes reported to police result in a conviction. And that's now, in modern times. Age of consent means below that age all that has to be proved is the sex happened, for a succesful prosecution.

In the Netherlands they have an age of consent that begins at age 14, but only if there is less than two years age difference. There's a lot of unwillingness in many places to consider that young people will be exploring, whatever the law or family and community say. The Netherlands seem to take a harm-minimisation approach, as they have also done on drug policy. Many other places see policy as about 'signals', for instance the baffling opposition to HPV vaccine which can almost singlehandedly prevent cervical cancer and one of the biggest causes of infertility. Opponents said it would communicate by giving it to children before they are sexually active that now they can be. That kind of complaint never seems to look for evidence, or be interested that human behaviour is not impacted like that. Similarly the death penalty does not lower murder rates, but advocates while pretending to care about consequences, in fact don't.

Sex for the mentally disabled is a challenging issue, in terms of ethics and moral philosophy. You have to work through a whole range of issues about values and autonomy, rights, risks of exploitation. And crucially it's an area a lot of people have strong intuitions about, that they are not willing to investigate or question. This isn't unusual, and so there has been a shift in philosophy from making declarations about what is moral, towards investigating moral reasoning and looking at practical ethics, especially in the context of medical decision making. This perspective comes under Moral Intuitionism, and can be investigated and challenged through discussions that generate 'moral dumbfounding'. See eg these papers Searching for Moral Dumbfounding: Identifying Measurable Indicators of Moral Dumbfounding, and critique of whether it reveals our moral reasoning to be irrational here A reason-based explanation for moral dumbfounding.

Here are discussions of some topics that challenge some common intuitions:

My TLDR: Different nations communities and individuals prioritise different things, which leads to different decisions. Shame, disgust, and status, are primarily not rationally allocated, but relate to culture, and game-theoretic emergent dynamics - like historical contingencies, moral panics etc.

Here are some articles which address specific issues around a group where we don't think people can give consent, but where simply denying them any sexual activity is in conflict with other values. Specifically, this topic suggests mental maturity isn't the only factor for consideration.

Masturbation suit lets people with disabilities fulfil their sexual needs

Disabled people can be taken to prostitutes by care workers, judge rules vs Disabled men don’t have a ‘right’ to buy sex

There just isn't a simple answer to your core question. As objective as we can get is probably focusing on harms and their minimisation. But in practice that leaves many decisions still to be made. So it's about investigating the process of moral reasoning, and how to order your hierarchy of concerns, towards making consistent and coherent decisions, with reasoning that others find compelling. That's why we need philisophy.

  • 1
    It is too bad that the question had to be closed, because this seems like a practical and relatable entry point in to the thicket of ethics and morals. Perhaps from here it could branch out to other areas people differ on. Finding common ground is probably more important than dictating rules, and you alluded to commonalities within some different cultural settings. A good start.
    – Scott Rowe
    Commented Dec 31, 2023 at 22:23
  • 3
    @ScottRowe: I'm voting to reopen, seems like a prime topic for practical ethics, exactly because it's culturally sensitive & awkward. We want easy answers to complex questions, & that is where we must enquire more deeply, & challenge intuitions.
    – CriglCragl
    Commented Dec 31, 2023 at 22:39
  • 1
    @CriglCragl thank you for your detailed answer, and for voting to reopen. This is my first time posting on PSE, so I'm not sure I understand why my question was closed...is there anything I should do to improve the post? Commented Jan 1 at 1:04
  • @DavidRaveh There are two things. One is to phrase it in the most neutral, academic, and scholarly way possible, so as to minimize the amount of controversy it incites. The second is to connect it with philosophy as much as possible: what is the core philosophical question, at the heart of the topic? I would say it is about the ethics of sexual relations, particularly regarding age: what human characteristics (relating to age) are relevant to deeming a sexual interaction ethical or not, and why? Commented Jan 1 at 21:51
  • 1
    @JuliusH. This is really helpful, thank you. It will take me some time to implement the changes you suggest, as I really don't know much about different moral theories. Commented Jan 1 at 22:31

The bare minimum of maturity would probably be "sexual maturity" that is "menarche" (for girls) and "spermache" (for boys). So first menstrual bleeding or first ejaculation. That is when your body is technically ready to produce children and which can be as young as 12-13 (on average) year old. Before that you neither have the development of the necessary body parts, nor the prevalence of the hormones that make people want to have sex in the first place.

Also worth noting that the development of both of these is usually not concluded at this point but goes on until the end of puberty by age 15-17 (on average).

So at the very least your reproductive organs need to be ready and you'd need to have sufficient levels of "horny hormones" so that you want and enjoy that level of intimacy and don't find the other sex (or the same sex) just "ugh" and the whole reproductive system as gross. That would probably be the biological side of that.

Though there is still a societal side of that and that doesn't just include laws forbidding to have sex. But in order to make an informed decision you should be aware of what sex is. So what you're getting yourself into. What boundaries you should set, look out for and respect, what's the link between having sex and reproduction, which is not immediately obvious but pretty consequential. What options are available to have sex without having children, what options you have in case something does not go as planned.

So even though a 13 year old could have children they are in a position in society where this is not necessarily a good idea. Insufficient education, insufficient funds, still considered a child and not yet full access to all rights and privileges aso. Though that is at least partially also a societal issue, due to the fact that things are structured, like there might be communities where it's normal that an entire village takes on the task to raise a child and where that is not seen as the responsibility of the parents or even parent alone.

And even if the people in question are physically capable of having sex and properly informed about what that means, what the consequences are and also horny enough to want all of that regardless of all that, then parents and society might still be in a weird position where on the one hand they need to respect the sexual self-determination of the child to make their own experience and where the repression of that can be an invasive act with harmful consequences, while where on the other hand they still have a protective duty for the child and sex usually comes with a situation of vulnerability and without witnesses, so even if we ignore the sex part of it, that might still be a dangerous situation.

Also with regards to societal norms you might cross boundaries that you might not even be aware of. Like idk past societies that valued virginity might render a woman unmarryable if she had sex before wedlock rendering her a liability for their family who might not be able to support herself due to lack of education for women and in consequence the inability to find employment. Or work in porn and prostitution might create a stigma for people pushing them to the edges of society (or it might simply not be a long term career as you might be too old once you're idk 30 or 40 but you're likely going to live much longer than that). Which is not inevitable by itself but consequence of societal norms. Which can add to or subtract from (maternal leave, child protective services, birth control and contraception, medial means to treat stds, etc) risk involved in having sex.

And that's just the average case, which is complicated enough, for people with a physical or mental handicap you probably need to look at that at a case by case basis balancing all these different rights and perspectives where, the drawing of the lines is still somewhat of a negotiation process depending on where you'd set the priorities.

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