The thing is: you can tell your 21-year-old self anything you like; will he/she listen to you?
When I was one-and-twenty
I heard a wise man say,
“Give crowns and pounds and guineas
But not your heart away;
Give pearls away and rubies
But keep your fancy free.”
But I was...
Study hard and don't waste your time chatting up women until you're nearly 30 - as you're not going to get anywhere with them
Live abroad - before you get bogged down in life's responsibilities