At a certain point in your life, you realize that you are who you are.
That isn’t to say that your life won’t change. Of course it will change. So will your personality, but not in big ways. If you’re an introvert, you’re not going to suddenly feel energized by hanging out with a room full of happy strangers who want nothing better than to engage you in mindless chitchat. And vice versa.
You may be able to change some of your habits, if you’ve got the willpower. Of course, if you don’t have willpower to begin with, you probably won’t be able to do too much about those habits, unless they’re going to kill you. That can replace willpower.
This is the stage at your life when you can be happy with who you are, if you accept it. But that’s the hard part of this process. You have to give up on some idealized version of yourself, and accept the being you are at the moment. You have to stop living in some perfect future, and hang out in the present.
But you can always get a new haircut.