I cannot emphasize this enough. And even then, be extremely careful with heavy lifts (anything more than, say, what your body weight would be at 20% body fat).
I worked regularly with an extremely good Rippetoe-certified coach. My form was better than most of the beginners you see in the gym. At 40, I was stronger than I was as a high-school athlete, and it was an amazing feeling.
But one day, a 245x5 squat set went very slightly weird. Two days latter, I had tingling and numbness in my foot soles. It turns out that I'd aggravated a relatively minor disk bulge at L4/L5 (about half the population has a disk bulge there). And now I've been in moderate pain for close to three months with very slow improvement.
The long-term prognosis is excellent, as far as I know. I will almost certainly heal. I know plenty of people who've done worse to their backs and who are fine today.
But heed my example: If you're going to do heavy lifts, especially deadlifts or squats, make sure your form is as close to perfect as you can get it, and remember that you can't eliminate all risk.
One thing I have noticed: There are no 55- to 70-year-old powerlifters in the gym. But there are old bodybuilders who've been lifting for 40+ years with only the rarest of injuries. They're careful, and they say things like, "I don't like the risk/reward on heavy squats." When I return to serious lifting, I'm considering on giving up on powerlifting and switching to a more bodybuilding-centric program.