Not to mention, 60 is pretty damn young. You're cutting off people in the prime of their maturity, especially with longer lifespans. Teddy Roosevelt died at 60 and one of his greatest regrets was that he peaked too soon, and that was a century ago
Changing age limits is just a bandage on a bigger wound, which is that US society struggles to produce quality leadership. But that's what dominating the world for a generation will do, it makes you soft.