I recently watched a batman classic animated film called "The Dark Knight Returns". In this universe, Bruce Wayne is an old, war-tested Batman who has almost seen it all. In this movie, he squares off against The Joker, and other members of his rogue gallery, but most famously the Man Of Steel himself, Clark Kent. The movie was great, and I would love to see it in live action. Here are my top 3 choices to play the old batman:
3) Micheal Keaton
Simple; Micheal Keaton was the perfect Batman ! Micheal Keaton's performance as Bruce Wayne and Batman in 1989's Batman and 1992's Batman Returns has silenced doubters and critics and left a legacy behind that nobody has lived up to yet (Christian Bale got close though). It'll be more realistic, the old batman donning the cowl and getting back out there. It'll also be cool to see someone reprise their role over such a long period of time.
2) Bill Murray
When it was announced that Bill Murray was planned to be Batman in a live action film, I really didn't care, but I like his sense of humour.
1) Sylvester Stallone
He's already in shape and has the body,and experience, plus his fighting movies like rocky and stuff, I think he'd be a good old batman.