Lisa is correct - the comment was pragmatic, not didactic. I don't know the actual median age of the YC applicant pool, but in my own anecdotal and unscientific experience (e.g., who have I met in person at events, or heard a pitch from) the median YC participant is around 23, and has yet to develop the familiarity with pitching that comes from years in the industry. Also, if program awareness comes from social networking or from university outreach, I'd expect a dominant concentration of 20-somethings in the pool.