Don't talk age! Age has nothing to do with it. One of my guys who started out at my gym is 87 now, and he still does ten bench-press reps with a hundred-pound dumbbell in each hand. He's training to set a leg-pressing record. I put things in the guy's brain way back when, and now he'll never get away from it.
I'm pretty fit, naturally. I do moderate exercise, and I try to eat pretty well and I think it has an effect on me. But hey, I'm putting on the insulin tire like everybody else, but that's just a function of getting older.
There's a certain cruelty to being on a big screen as your eyelids start to sag and your hair falls out and turns gray that you either have to be able to handle or not. What you can't do is try to force yourself into roles that you could have played or would have played ten years earlier.