1) I've been strength training since I was in the Army. Wife and I joined a local gym in '79. Hindsight. Still at it twice a week for an hour. My wife had never done anything physical except hike. No injuries, no problems.
2) You got a crummy coach. Well, be generous, an idiot.
3) My aunt started strength training at 80. Went really well. Got stronger and stronger, no injuries, had never done a bit of any sort of physical exercise in her life, zero talent, sedentary ancestors. And fat. Now 87, lost 30 lbs., deadlifts 90 lbs., heaves truck tires, walks without a cane..
All that said, it is a cautionary tale. Be very careful picking a PT. We have maybe 6 PTs who use our gym, all certified of course. They start out with a lot of strap and band and floor work for folks who don't have history, almost no free weight work.
It is interesting how cycling and running both use a very limited range of motion and muscle use. Transitioning to full body work is a big deal. For someone starting, I recommend just using
Core Advantage for their first year. (cheaper on Amazon)
I know a lot of people near my age who've contracted all sorts of injuries and disabilities by simply ignoring the fact that our muscles go away, our tendons and connective tissue gets weaker, and our cartilage goes away, all of that from disuse. I weigh about what I did in the Army, use the same weights, and have managed to stay uninjured even though I ski, backpack, and do some construction. Oooh, I take that back. I did have a back injury maybe 10 years ago. I hadn't been going to the gym or even riding much that fall and then I went skiing with a Frenchman who used to tour with the Dynastar team. I was carving really hard on a very packed slope, lots of g's, and I felt (and heard) my back go blewy. Yeah, that's when I did Core Advantage for a year. No problems since.