^{I don't belong to the group of youths, but one does not need to belong to the particular group in order to defend their interests, like in the case of animal rights movements. Also, I belonged to it, therefore I have some experiences.}

Let us look on legal drinking age laws. I know why they exist, but these laws are easily overcome. I would say they are like obstacles rather than justifiable prohibitions. Yet, adults do not face such obstacles. It looks like oppression to me.

There also are other examples such the driving age, the age of consent or age of watching porn. All of these appear oppressive by me. If you can drive well, your age is irrelevant. If you want to have sex, your age is irrelevant. If you want to watch porn, your age is irrelevant.

Is there an ethical theory that rejects such laws as oppressive ? If there is, what is its name or label ? I am looking for references.

I do not assume there are no differences between youths and adults, I just say this age difference is irrelevant, just as the difference between males and females is irrelevant when speaking about feminism (in the form of universal rights).

As this paper says (link provided by @Conifold), adolescents on average are more impulsive, yet then we should merely to prohibit the driving for impulsive people, not for adolescents, why not? There indeed can be adolescents who are less impulsive than average adult. If it is wrong that these differences are foundations for these laws, then what are the arguments for existence of such laws?

Regarding sex, I assume informed consent is a much better solution than age of consent. Anyone, regardless of their age, can give consent if they know the potential results of sex: pregnancy, STDs, injury caused by too rough sex, etc.