I would say when you no longer enjoy it. It defiantly takes the pressure off knowing you can go at any time. I just can't see doing it past 60. The money is great the job is easy but the main thing, unfortunately, is that the work has become meaningless. Didn't used to be that way, but that's irrelevant, it's not going to change, only get worse. So I can continue to feather my nest a bit, relax a bit confident I can leave at any time the management morons can longer touch me. I can do two. I sure couldn't do twenty in this screwed up industry.