The management at airlines are behind the push. Reducing training costs for two years is a big savings for all airlines. They're probably making a lot of campaign contributions right now, spreading it around among politicians they expect to be in office next year - good timing since it's an election year.
They'll trot out some willing pilots to testify that raising the age is a good thing to help alleviate the shortage. They'll get AARP support on it to oppose age discrimination. They'll point out that it will save the social security trust fund money.
But all of that's kubuki theater for the public - the political contributions will ensure passage of an age change. We're just pawns in the game.

My guess is that ICAO's rules will also change within a year or two after the US. Because you can bet there will be plenty of palms greased.