The chart above reveals two very interesting things -- one obvious, the other less so but just as important.
Let's start with the obvious. The fact that seven in ten people aged 18-33 support the idea of allowing gay people to get married suggests that the trend line on the issue overall is headed in a very clear direction. Even if you buy the idea that some of these millennials will get more conservative -- on a variety of issues including gay marriage -- as they age (and there is some data to suggest that's not going to happen), it still seems very likely that a majority of millennials will support same sex marriage as they move into their 40s and beyond.
Now, the less obvious. Start in 2004 and chart how support for gay marriage has increased over the last decade across all four generational groups. Among the silent generation -- the oldest living generation -- support for same sex marriage has nearly doubled in that time. It's move upward by nearly 20 percentage points among Baby Boomers and Generation X'ers as well. What does that tell us? That views on gay marriage aren't solely determined by age. Yes, younger people are more supportive of same sex marriage than members of the silent generation. But there is upward movement in support of gay marriage within each generation as well. That sort of inter-generational movement suggests that the fundamental culture conversation on gay marriage has shifted and isn't likely to shift back.
Charts like the one above should make one thing very clear: While the cultural war over same sex marriage will likely continue on for some time, the political fight on the issue is effectively over.