I had a lower back injury at about that age resulting in a ruptured disk. It was debilitating and required surgery. The surgery worked wonders but, unsurprisingly, I've had intermittent back trouble in the decades since then.

I've had two periods of my life where I've been free from back problems for extended periods. The first was when I was doing aikido. There was some minimal warm up stretching, but the main thing was that practice involved a lot of range of motion. Despite seemingly bad things like awkward positions and getting thrown and hitting the ground hard, I had no back problems at all during that time. The second time was when I was lifting free weights. Squats and deadlifts (done correctly) strengthen the support infrastructure for the back (and everything else). During both of those regimens I also lost a fair amount of fat. (I actually gained weight while lifting but my wife remarked that I looked thinner).

I think that many kinds of exercise could have similar effects. Yoga, anyone? Maybe Tai Chi? Man, I need to get back to doing something regularly again!