I had lower back pain since I was 19, and no doctor could help. They just said "you have to live with it", which was not really comforting. I couldn't lift things (still cannot), and there were times the back hurt in every imaginable position. I felt vertebrae slipping in and out, like a sort of hernia, but luckily it never went so far. Once I flew from Germany to Turkey lying on the floor of the plane because I couldn't sit anymore. In winter, I went around with rheuma belts at the age of 25...
I tried some special gymnastics for strengthening the back muscles, but they didn't help. And then, at the age of 38 I started aikido, and the lower back pain just went AWAY. It took maybe some weeks or some months, I even don't recall, but now it's just GONE and never came back. So that is some miraculous healing, or maybe aikido just helped to relax where I didn't know how to relax before?
Back pain never affected ukemi. In the beginning, I was so much afraid of falling onto my head, which I did several times, that I didn't worry about the back, and once ukemi came out as it had to, back pain was long gone.
But one month before I had a rupture of cruciated ligaments in the left knee, also due to aikido, and as Abasan rightly said - it was not due to aikido, it was due to very wrong aikido. I made a stiff tai sabaki tearing my partner in an improper angle, so maybe it served me right.
So my advice would be - just start, probably it will do you good!