It's a simple matter of hiring someone to stand behind him and pull on his face
When David Letterman told Adam Sandler on “Late Show” that he still looked as youthful as when they'd first met, Sandler let him in on a little secret. And it's not the same secret that most of Hollywood uses to try and maintain their youthful looks. Sandler is absolutely against plastic surgery. He doesn't want his kids to get the idea that this is something they can do because they saw their daddy doing it.
Instead, he has a trick that he does for close-ups in his films. “I'll have an assistant sneak up behind me,” he said. He then has them hold the sides of his face and pull back. It's a simple home remedy anyone can do, so long as you have someone willing to stand behind you and pull on your face, and you don't care about all the weird looks you're sure to get.