re: point 1
I'll respond to the ageism thing first; I'll just speak for myself; I'm inclined to value an older person's ideas more than a younger person's. Generally, with age comes experience and often wisdom. Sure, there are teenagers way beyond their years in terms of intelligence and wisdom and spirituality and life knowledge. Maybe there's a bit of a respect issue for me; I'm very liberal and open-minded and very INTP too-- so that I can value ideas in and of themselves without letting the nature of the speaker skew my perception of the idea. However, imagine when your parents told you something, and you ignored their advice. Then, when your best friend tells you the same thing, you take your best friend's advice. Extrapolate that same effect to ageism. If Kim Kardashian says "Yes, we can" vs Barrack Obama saying "Yes, we can"-- it seems to have a whole different effect. So it would be totally ignorant for me to say that it doesn't matter who speaks an idea; very often, although we don't like to believe it, it really is not the IDEAS that we value, but we place emphasis on the SPEAKER who speaks the idea.
and, responding to why a guy would change his (or my) behavior once it is found out the other party is a girl-- it probably is illogical, but the penis doesn't have a brain. If guys thought logically, they would never get laid. That girl will probably not sleep with me, so I should not hit on her. This girl on the internet is not even in the same country, we will probably never meet, and there's a one in a million chance we'll even get beyond first name basis... BUT! the same energy that a guy taps to walk up to the girl of his dreams (who will obviously turn him down) and goes for gold and attempts to get her digits, is the same illogical nature that baffles you; it is not going to be understood with "T"
re: point 2, pulling out the chair being offensive for you
Well no one's going to blame you for feeling one way or another; but I think your feeling is misguided and misdirected. Why not feel flattered? It becomes logical when you understand guys are just doing what is in their best interests (to get laid). Now if they knew YOUR personal preferences then that behavior would be counterintuitive, and you'd probably be a "let's split the bill" type of person... but often it's just better to play the odds and appeal to the knight in shining armor gentleman-like behavior.
I actually can't really recall if I've pulled out a chair for a girl while on a date, it does seem a bit old school, but I would defend the practice; I'm not conservative by any means-- but I do have a little sister and I'd probably approve of a guy that proved that chivalry is not dead. Maybe if you press me for a more logical explanation I could give one to you later.