This issue came up in the comments to Ilya's post below, so I thought I'd point to a post of mine from a year ago on the subject. Short version: National Opinion Research Center surveys have for years gathered information on whether people believe that homosexual sexual relations are "always wrong" (the other possible answers to the question are that such relations are almost always wrong, only sometimes wrong, or not wrong at all). Here is the data from those surveys for 1973 and 2002, as reported by an American Enterprise Institute paper:
|60 and over||89||68|
This suggests that the group of people who were 18-29 in 1973 remained on average about as accepting of homosexual relations 29 years later, in 2002. The group who were 30 and above became slightly more accepting of homosexual relations, though only by a little. Neither the gay rights movement nor life experience seem to have made much of a difference to those age cohorts' attitudes. (Obviously they may have affected many individual members of each cohort, and could even have pushed tens of millions in one direction so long as they pushed a comparable number in the other; I'm speaking here of aggregate effects.)
Of course, it's possible that the attitudes about specific gay-rights questions (same-sex marriage, antidiscrimination laws, and the like) might be affected by age, even if attitudes about the morality of homosexuality are not. If you have similar age cohort studies that relate to those questions, I'd love to hear about them.
For more pointers, see the earlier post.