Being asked to prove that you belong in the premier line b/c you're young doesn't seem like too big a deal--you'll miss this and being carded for liquor soon enough. Being treated differently in a substantive way is definitely a big deal.

When you're older, you'll be able to search better. Just kidding. Here are a couple of threads I found.

http://www.flyertalk.com/forum/Forum50/HTML/003578.html

http://www.flyertalk.com/forum/Forum50/HTML/000983.html