I've not watched him since he left the club and players do "age" differently. I would imagine however that a lot of clubs view a 30 something keeper as in his prime. It would appear Arsenal do. So i'm not so sure his best days are behind him just yet.
Although he's probably going from 40k to 100k a week. It's easy to say he'd be better off staying as a first choice and earning less. I doubt many would turn that down. I know I wouldn't.