You have a magic pill, which de-ages you by 20 years. You can take it once in your life only, so long as you are at least 20. What age — past, current or future — do you reckon is best to take it?
It depends whether I can somehow go back to the body of a 20 year old but keep my current 40 year old brain. I'm not going to pretend the majority of my improvements in patience, empathy, humility, work ethic and dgaf-ness are me consciously maturing instead of improvements in brain chemistry.