Hi Jeff,
I'm Josh, and have a severely damaged lumbar spine from my Army service. Yeah, even though I'm forty now, my mom hates the fact that I still skydive.
I have never felt pain in my back from civilian skydiving because I have always used a good PLF when I land (and don't jump at night at 800 feet with 350 pounds of gear!). I only landed once on my feet because it was required for the Class A USPA license.
"Civvie" chutes give you nice, soft landings, the free fall is just plain fun, and doesn't hurt a bit either.
The danger of hurting your back could happen in your own bathtub--a mistake. Just carefully think about your landings, practice, practice, practice PLFs, plan a good landing, use what you've got between your ears, and you'll be fine. Just remember, like downhill skiing, you're moving really fast, have other people and obstacles to avoid, and always need to have an alternate plan (like most drivers ought to).
Blue Skies! I love the freedom, mental energy, and concentration that go into skydiving. I also enjoy the people I meet at skydiving centers, especially single women.