I think a lot of this disappointment at 40 comes from the fact that a lot of kids (especially in the US) were told silly things like "you are special" and "you can become anything you want to become". So a lot of boys grew up with the idea that they were going to be Richard Feynman + Bill Gates + Wayne Gretzky rolled into one. When that didn't pan out, they didn't understand what happened to them. Nothing happened - you were born human.

This whole "you're special" thing wasn't always here, it's a relatively new thing.