Answer: your age. Seriously, how many decisions do you make with that number echoing inside your head? Too old to take up an instrument? Or study? Or have a change of career? Too young to marry? Or settle down?
Once you hit 18 it’s time to throw that number away. Once you hit 18 you’re a grown up and your life is your own.
Change career. Move. Study medicine. Or archaeology. Write a book. Paint. Travel. Take up violin. Fall in love. Learn to ski/tango/meditate/fly/sing.
Do whatever you passionately want to do. Forget your age. It’s just a very silly number. A ridiculous number. An excuse.
There are no limits to who you can be unless you make it so.