What is the best advice you could give to a 21 year old?

Give up on everything in life except our goal. No obligations to friends, people and family unless you decide to give them your time. 21-25 are the most important years in terms of work. You can always party after you get older too.

If you did nothing except a few mindless jobs and partying then you're fucked. It's like building muscle on your body. It gets harder and harder as you age.