Here's an idea - an annual concert billed as some sort of tribute or recognition ceremony - some term that indicates that the stars may be past their hayday - stack the place with your and their family and friends - give each performer ten or fifteen minutes, maybe have some younger volunteers perform a few of the old-timers' hits - pay the old guys whatever you can out of what I'm sure is your inexhaustible slush fund, make a speech about their tremendous contributions, etc.

Several advantages to this: when they're asking for gigs, you can say, We really want you to be part of the Gala in April, blah, blah; they may take such an occasion for what it is - a kindly and respectful way to tell them their day is past, and graciously bow rut; you can feel that you've done your part to honour their contributions and spare their feelings; also, it doesn't have to be part of your regular concert schedule. It could be a good time too.

Whether or not that seems like a workable idea, I think with some creative thinking there may be some way of dealing with the situation other than refusing the gig flat out. Here's another possibility: "Joe Smith is coming in November, and he always liked your music. He said he'd really like it if you'd come and do a set with him, and we thought that would be a good idea." (Better run that one by Joe Smith, though!)

Who was it that said "old age isn't for sissies"?