It's been 5 years since i first responded to this thread, still i a curious and interesting question to me.
i do subscribe to the spectrum theory of human sexuality, and i see that spectrum as multidimensional, not just linear. I.e., i suspect there are infinite variations on the generalized labels we have for communication like: "straight, gay, bi, etc.."
i can see age as a factor going either direction on this question. I.e., i can see some men being 'more' straight as they age. But maybe it isn't a matter of any of us being more or less, but having gotten to a place where there are more or less boundaries? Some cling to their notions, ideas, identities- as they age- to maintain a sense of security. Maybe that's a part of dealing with mortality. On the other hand, some may want to experience newness, difference, as they did earlier in life when they had fewer experiences.
i think it's a complex question though, and don't think there's a yes or no answer, that individuality plays more into this than age?