Holy wow. Bob Mould is 51 years old and brings more fire and grit to every performance than any 20-something punk frontman has in the past decade. Dude has more than half a century under his belt but his presence has not aged a day since the '80s. Very few can lay claim to that kind of agelessness, especially in the punk rock world. Watch Mould slay on last night's Letterman below (bonus feature: watch Letterman overenthusiastically pronounce Hüsker Dü multiple times).