True, but is much more important for "20-year-old-whizzes" to learn than to senior people, at least if you want to accomplish more than those people.

As a 1-year junior with crushed dreams by a proto-startup project and now working in a technology conservative environment I can say there is so much to learn in the first years (from bad or good examples, with or without mentorship) that everyone should review his attitude. Of course always keeping the ambition and with the goal of accomplishing the most.

To have success while young and without experience you must be allowed to fail, and to fail a lot of times. Out of frustation of course, I'm starting to believe it's really hard to have success in the early times. Of course close mentoring as in Y Combinator should help a lot!