J'ai trente ans!
There are always different ways to calculate how long have you lived in this world.
Somehow, this kind of milestone could be achieved without too much efforts as long as you maintain your body components well and no tremendous luck required.
In Chinese, at this age, you should be able to "stand." Starting your own family, advancing your career, and things also start to be regarded differently eventually.
Officially, young is not a right adjective for you anymore. You would be less excited when some pretty girls looking at you than when you find you get a promotion or bonus.
Dreams are still there, but you would start to concern if knees and shoulders would break before realizing those goals.
However, after some friends' reminders, I found I haven't been that old yet. I will reserve all my sad feeling until next year.