I think the claim that "meaning of life" is new in philosophy may be (a) possibly true in the narrowest sense and (b) empty in any real sense.
First off, it might be possibly true in the narrowest sense. "Meaning of life" is somewhat a neologism. I don't recall it appearing in any classic philosophical texts, but there are at least two reasons for this. First, it has a certain interpretive flavor to it to imagine life has a meaning that existed under realist metaphysical accounts but falls away under nominalist, linguistic, and skeptical accounts of metaphysics. Second, the unit "life" is not always the most well-defined idea.
Now, for why I think even if the above is true that it is trivially true. Among those metaphysical realist accounts are examples like Plato and Aristotle.
Aristotle looks at the "end" of all sorts of things including human life (spelled out in the Nicomachean Ethics and Politics). Plato seems to have an account of what humans are for in the Politics but also in the Meno. The Analects attributed to Confucius also seem to give an answer to the meaning of life (which I will abbreviate as participation in family and culture through ritual). We can keep going and find that many views have an account of the meaning of life even if they don't use those terms.
Or if we mean by this "meaning" something more theological in orientation, Plato still has one of those. We and everything else in the universe have the meaning of being shadows of the forms. Aristotle that we are parts of a larger social whole or that we are seeking our final end which is determined by our nature.
The term might have gotten a revival post-existentialism or during the existentialist period as a re-evaluation of the purpose of life without metaphysical underpinnings and the analysis of how we could make sense of that, but its's not the first time people have tried to make sense of our world.