With the Supreme Court hearing gay marriage cases today, the new poll from CBS news on marriage equality is striking, and strongly suggests it’s in the interests of the GOP to evolve on the issue already.

The poll’s toplines find that support for legalizing gay marriage is at 53-39, with a stunning 33 percent of Americans who support marriage equality claiming they once held the opposite view. That alone underscores how fast the culture is changing on this issue.

And here’s another key tidbit underscoring cultural movement: There is a sharp generational divide among Republicans on the issue. Overall, 56 percent of Republicans oppose legal gay marriage.

But I asked the CBS polling team for a breakdown by age, and the result was that among Republicans under 50, a plurality of 49 percent supports legalizing gay marriage, versus only 46 percent who oppose it.

What’s more, the poll also shows that support for gay marriage is even higher among the voter groups that Democrats are increasingly relying on. For instance, among voters under 30 overall, a stunning 73 percent back marriage equality. And among college educated whites — a key pillar of the Democratic coalition of the future — 68 percent support gay marriage.

All of this dovetails with another recent poll finding overwhelming support for gay marriage among constituencies Republicans need to improve their standing among, such as young voters and Latinos.

The interesting thing here is that even the Republican National Committee’s own diagnosis of what ails the party recognized this generational divide. It said: “Already, there is a generational difference within the conservative movement about issues involving the treatment and the rights of gays — and for many younger voters, this issue is a gateway into whether the party is a place they want to be.”

Today’s poll bears that out yet again. Yet as Jed Lewison points out, RNC chair Reince Priebus has now explicitly confirmed that the party won’t be changing its stance on the issue, and instead will continue to adhere to the party’s platform, which declares that marriage must be upheld as the “union of one man and one woman.” This, even as younger Republicans no longer hold this stance, and only the older ones do.

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UPDATE: Another poll bears this out. The recent Washington Post survey finds that 52 percent of Republicans and GOP-leaning independents aged 18-49 support legal gay marriage, versus only 43 percent of them who don’t. Check out the Post’s cool chart on this.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.