Hey Fish, Unser Sr. won his last 500 at 48, that's not too shabby, especially considering he only entered three races that year! (Indy, Michigan, and Pocono)
Yeah, A.J. couldn't win at darts at the end of his career, but a lot of that was from various injuries. The guy _did_ win LeMans, remember.
Mario won his last race at 53, true, but that was at the end of the 5-year drought he'd been suffering since Cleveland '88... He was always strong at Phoenix, it has a lot of similarities to his home track at Nazareth.
I'm enjoying this because there's no wrong answer!