'You'll Never Be As Young, Cool, and Careless Again'

I forgot the whole exact phrase of what the club owner was saying at the end of this movie, but is he ever so right! I was about as carefree as the main characters in this movie at that age. For those of you who are older than 23 (like myself), what things would you change if you could be that age again while knowing the things you do now?

I'll start it off:

1) I would've taken my female relationships more seriously - At that age I used to date older women and then brush off the relationship once the woman fell in love.