George Will is wrong.
Nope, he's correct - the evidence from innumerable polls is overwhelming.
The core of the opposition to gay marriage (and marijuana legalization) is quite literally dying by the thousands every week.
And there's absolutely nothing that can be done to stop that.
And unlike some other Left-Right age trends (such as growing opposition to taxation with age, more concern about fighting crime, etc.) a 25 year old that supports gay marriage today is probably going to still support gay marriage 20 years from now.
Simply putting your fingers in your ears and screaming loudly isn't going to change reality.