I have had a lifetime of this exp both ways and with women. So I feel qualified to comment.
1. Yes there were (and still are) codes of dress that identify sexual preferences, but nowadays it is so wide that it is confusing!!
2. My view is that every guy is capable of being both. Just depends on his experience and enjoyment to date.
3. It is all down to chemistry and mood during the activity....
4 No form of penetration need to be painful (though sometimes it can add to the pleasure). The more chemistry and compatability there is the closer the two humans can simply connect.
5. Internet has forced the issue of being clear about whats what. So it is rather unnatural. Better to be openminded until real life steps in only then will you know if it is going to be good!! I have been pleasantly surprised in my time but much prefer the real life situation.
6. I love being bottom because it is the ultimate expression as a male to submit to another male sexually. Very different to women, whole set of different dynamics.
7 Sexuality is a whole spectrum of colours, it cannot nor should be pigeoned holed or treated like a shopping list of demands. It is an exploration of experiences and moods.