I'm a bit late to the party but if they still want to perform and can get an audience, why not?

There might be an argument that older performers should give way so that younger musicians can have an increased opportunity to progress and succeed. I don't necessarily agree with that either but it doesn't apply here.

We get endless discussions and debates, for instance, about folk clubs which book the same old artists while younger acts don't get a chance. However, even there, if an artist(s) can draw an audience and is still popular enough then age shouldn't matter. Of course, a club committee or booking agent should also consider acts on their artistic merit too. It shouldn't all be about "bums on seats".

However, the above doesn't apply here as the tours and concerts are being promoted independently. So, they aren't holding any other artists back or preventing them from getting gigs. So, good luck to them.