Advice to my younger self and you after 20 years in programming

No, I don't agree. There's more to life than money. In money terms, you may have wasted your time. Did you learn anything? Did you have fun? Not a total waste, then.

Look, you can make a side project into an obsession that eats your life. Don't do that. But for more reasonable levels of "side project", they have a place even if they never make any money.

Passion projects are what really matters. I think making everything about revenue is what's wrong with the whole world, and I think feeling the way you feel (you wasted your time) is a direct symptom of living under such a parasitic economic system. Our right to access the basic necessities of life is dependent on our willingness to turn a profit for some already-rich person. You didn't waste your youth, you used it well. It would have been a waste to spend such a wonderful time working yourself to death.