Easy one. To my 21 year old self. Don't give up cycling! Just because you're now working full time doesn't mean you have no time for anything. You're still single, have no kids and have your weekends free so keep at it. Don't give up and end up starting again 12 years later.
PB is the most sensible person on here.
Further to the above.
Even if it does make you blind, it is worth risking one eye.
To my teenage self:
. And don't go to university to study f'ing Politics.
"Listen to everyone, trust no-one, decide alone."
I wish I had ben less easily led when I was younger, and more independently-minded. I made all manner of life and lifestyle choices which, at the time, I thought were the default, but actually were nonsense. What makes this advice useful to my younger self, is that I knew that the choices I was making and being made for me were nonsense.