I'm mostly looking forward to faking senility and being able to get away with going out in public with no pants. But I think I have quite a bit of time before I get there ;) I still haven't even hit 30, but I believe I am prematurely aged! Having 2 kids probably helped with this process ;)
You're not growing old, you have grown up. IMO you've settled into blissful responsibility. At the core, you have eliminated selfishness. Consider yourself extraordinarily lucky to find this place at such a young age. Enjoy the next 60+ years.
I keep telling my girlfriend Im becoming an old man but I'll never stop listening to refused. I told her to smother me in my sleep if I can't listen to them anymore.
Responsibility ages you. Or I should say matures you. Priorities shift, and what's important to you changes. Don't forget to have some fun. We don't stop having fun because we grow old, we grow old because we stop having fun.