I think that Ralph said it best...delegation. If Marv had the right coordinators, experienced and strong, it could work out.
Slothrop...Warren Buffett is 75 years old, Jack McKeon won a World Series at 73, Connie Mack managed until he was 88 years old, Ben Franklin helped write the US Constitution at 81 years old, I could continue, but don't feel like Googling any more.
Hey, why not? He's healthy and rested.