Just turning 25 a few months ago, I'm one of the older-younger people, I guess. Having been Platinum on AA since 1995, and Elite 1 on TWA since 1996, I've had some hassles in the past (like, "This is the Business/First Class line, may I see your ticket?" and other such issues), but I typically excuse them as being inexperienced staff. With the advent of younger frequent flyers (and lots of them being dot-com geeks), I have gotten less of that in the past 2-3 years. Most of my status comes from personal miles, as my business miles usually don't add up to over 20K per year, so my tickets are not always full fare (but some RTWs here and there don't hurt).

It does happen. Let me tell you, it does. I've been with business colleagues who have been 'profiled' both at check-in and at boarding because they look young, and the airline staff has been apologetic and has admitted that they profiled him/us because he/we looked young (this being AA, BA, and UA).

I don't know. I typically always wear (at a minimum) a button-down shirt, pants, and non-casual (though comfortable) shoes when I am travelling Business/First, so it's definitely not for what I wear. Many of the international flights I am on - I'm better dressed than some of the other Biz/First passengers. :-)