Old bands, for how long?

Last night we went to see “Earth, Wind and Fire” at the Deer Valley amphitheater. We had no particular expectations, but were really pleased by the forty year old R&B group. The three main protagonists are almost 60 years of age and one wonders how long they'll be able to deliver the major effort required to show up on stage and do more than just produce a decent show.
Do they still need the money to remodel their Los Angeles homes, work to pay the bills or simply perform because showmanship run still very deep in their blood? I hope it's the latter, but who knows... I don't think we'll ever see them again in our lifetime, but their performance was stunning, we had a great time and realistically, thanks God these guys are still around otherwise we'd only have Lady Gaga as an option...