I figure that I might have - at the outside - 25 years, though

the likelihood of more than 20 in which I might be really productive is scant. So say 20 years, in which to do 60 or 65 years' worth of work. Clearly I can't get it all done, so I have to pick and choose, and that means I'll have to cull some stuff before it even gets to the idea stage. I guess I'll try to cull the bad stuff, which means that 20 years should be plenty of time.