The 20-year-old is, maybe, just like you at that age: eager and smart, but lacking experience. Making bad decisions, bad designs, bad implementations left and right. Just like you did, way back when.
But you have made all those mistakes already. You've learned, you've earned your experience. You are much more valuable than you think.
Source: Me, I'm almost 60, been programming since I was 12.
I think the idea of meritocracy has died in me. I wish I could be rewarded for my knowledge and expertise, but it seems that capitalism, as in maximizing profit, has won above everything else.
You are rewarded for something that is useful to the market, i.e. to other people (useful enough so they agree to pay you money for it). If something you know is no longer useful, you will not be rewarded.
It was true 100 years ago, it was true 20 years ago, and it is true now.
But you have made all those mistakes already. You've learned, you've earned your experience. You are much more valuable than you think.
Source: Me, I'm almost 60, been programming since I was 12.