I first learned to play bass. Upright, acoustic, of course. Then guitar and then banjo. I haven't played a bass since 1960 but I still play guitar once in a while and banjo, constantly.
I think that you should play the five string banjo, old timey claw hammer style. It is true that few will want to have you play with them but think of the many hours of sweet solitude you'll be able to count on.
Later when you are in your dotage, you'll still be able to play the banjo because it requires so little physical effort to do so. As your voice cracks and fades and your playing becomes more and more basic you'll begin to sound like an undiscovered "source" and you can spend long periods of time talkng endlessly about the good old days.
Works for me:)