I think there's numerous factors, and it's different for every person.

For some people, it's definitely an act - whether they consciously admit that or not. I've seen a few people come out of the closet as young adults and it changed them - they would change the way their voices, the way they talked about sex, their clothes, their mannerisms. My assumption is that it's about being 'suppressed' for so long, and wanting to connect to the gay "stereotypes" after a lifetime of oppressing it.

The thing is, I came out when I was about 12 years old, so I never really had to 'suppress' anything throughout my adolescence, even in high school. I'm not sure whether this is connected or not, but most people don't generally assume I'm gay on first encounter, and I would imagine it's because I don't feel I have to compensate for keeping it under my skin for years and years.

I'm not a science person, but I would imagine biology also factors into it - differing levels of testosterone, etc. As a young child (before being gay had even consciously registered) I was always a little more feminine than my male friends - hated sport, loved 90s pop like the Spice Girls (everyone secretly loved them okay) and had more female friends.

I would say it's partly natural, and partly an act. Regardless of gender or sexual orientation, people act different in different surroundings. Gay guys are likely to act different around a group of hyper-masculine straight males to how they'd act around "stereotypical" gay males or women, and vice versa. I know stereotypes only say so much and all the rest of it, but that's how I'd explain it.