Let's see...if I were in my late 50's, playing better than I have in my entire life, arguably as popular or perhaps even more popular than I'd been in my whole career, and still putting old and new asses in the seats why would I think even about quitting? That'd be nuts. Honestly, its not like they have a super difficult lifestyle. Chartered private planes, finest accomodations that can be had, all the family and friends I have as close or distant as I want, golf wherever whenever, riding wherever whenever. What they could do is work like Metallica..one week on working every other day, following week home (or wherever). Why would you ever stop unless people stopped showing up, or you were physically unable? I think if they stopped they'd miss it quickly.