That's funny, I'm 41 and planning on setting up my brakeless track bike for the road again this afternoon (changing the gearing to 42-17 and switching from drops to a wide riser bar). If it goes badly I'll think of your warning.
I found a cure for my own lower back pain last year.
I had dealt with back pain throughout most of my 30s, and had self-diagnosed it as a bulging disc. Every few months I would lean over while brushing my teeth, or sneeze weirdly, or bend over to tie my shoes, and my lower back muscles would spasm and I'd be laid up on the couch for a week, taking muscle relaxants.
Early last year, I slowly came to realize that I had an unconscious habit of constantly holding my stomach in and tensing my abs. After unlearning this habit, my back pain is almost completely gone, and I haven't pulled a lower back muscle in about a year.
Picture the downward force generated by sitting on the bicycle causing the rear axle and bottom bracket to spread away from each other, causing the seatstays to break at the seat tube. This is what chainstays prevent on a complete frame.
which I'm still getting used to