I've just turned 65. My back is fine while I'm playing but kicks in big time at the end of gigs when I have to get down to unplug the pedal board or extension leads. I'm starting to develop a strategy now where the first thing I do is take the bass out to the car at the end of a gig. That little walk about seems to help to get a bit of gentle movement into my lower back. I've also got a rotator cuff issue but that is actually helped by lifting stuff with my arm pointing straight down so that's not too bad.
P.S. I've agreed to help some friends (who are doing a self build) tomorrow. Pouring a 180m2 concrete slab. Half of the 'crew' have dropped out at the last minute, so what I thought might be quite an easy day doesn't look so good now. Dreading it to be honest but I'll give it a go.