I'm not sure that the tech industry is particularly ageist against the young. Yes, a 17-year-old web designer may find (s)he doesn't get much respect from the tech industry, but, well, a 17-year-old anything won't get much respect from any industry. In our culture 17 is still a kid, and expected to do things like deciding that it's too hard to work and go play video games instead. I don't agree (my opinions are complicated, I don't merely believe the opposite, but that's certainly not an adequate summary), but I'm in the firm minority.