Some of this started to happen in late 20s. You get the idea
  1. Starting to accept what you are not
    I'm no longer interested in trying to be good at partying for example. I am not.
  2. Can afford better stuff
    Things I no longer get the cheapest version of: Beer, wine, beds, apartments, olive oil, fruit.
  3. You don't need your parents to pay for your vacations
    Related: I can go on vacation without my parents
  4. Less acne
    Maybe because I can also afford better skincare products?!
  5. Feeling truly comfortable when/if people don't like me
    It's cool. Someone else will probably like me. I can talk to them.
  6. No longer drawn to bad emo pop
    I can squarely leave Dashboard Confessional in the rear view
  7. Sex starts to get really good.
    A decade or so of practice really pays off, for you and for your partner(s).
    Suggested by @gabimoskowitz
  8. Having an easier time saying no to stuff you're not into.
    Kind of a corollary to your first point, in my 30s I got way better at politely declining invites/suggestions that didn't sound fun to me rather than grinning and bearing it.
    Suggested by @mandi