I think it's a mixture of both nature and nurture. I am bisexual and knew from 5-6 that I liked both males and females. I didn't really understand relationships at the time so wouldn't have known the terms for it but it was definitely at an early age. I think the opinions lie around the following questions:
Am I hanging around with women, gay men etc because I'm gay?
Am I gay because I'm hanging around with women, gay men etc?
I should point out that, in my experience, I used to hang around with girls all the time during primary school. Not entirely sure why tbh, it just worked out that way. Not trying to say there's a stereotype of gay men in the above questions however I think this is the point. There is no 'one size fits all' solution to this. People can live in the most homophobic of families and communities and still say 'I'm gay' (or if they choose not to say it, know inside that they are). This suggests to me that there must be some nature involved as well.
edit: words are not 'hijacked', words evolve. There's a difference









