I don't believe that the majority of people choose their sexual orientation whether it's gay. straight or bi. I think what we ultimately do is accept with what nature has gifted us. Therefore, I believe a gay sexual orientation is definitely nature. Where nuture comes to play is in how we deal with our sexuality.
I was in my early 30s when I came out. It took me that long to realize that being gay is not something I chose, but something I am. It's amazing how freeing stepping from the dark into the light can be. When I stepped out of the closet I vowed never to go back in. I did not choose to be gay, but I did choose to accept and celebrate the fact that I am. I have never regretted my decision to live my life as an openly gay man and if my being gay bothers anyone, well that's their problem, not mine.