Getting started with long distance rides...

Aye, of course. I was being flippant. I also have a bad back, and cycling's about the only thing that doesn't make worse - I can't imagine having the sort of bad back that would preclude cycling, it would be awful. Maybe speak to a physio to get some preparatory exercises for strengthening, etc?

+1 on speaking to someone about getting the right prep exercise. I have a collapsed disk which pushes constantly on a nerve, I didn't look after it properly when it went a year and half ago and have now spent a month without riding and am facing the possibility of surgery as nothing else has worked.

I would generally say if people have any back pains, get some advice on your bike fit and riding routine immediately unless you want to end up walking like you've just followed through like I do at the moment :-(