Getting started with long distance rides...

I know what you say, but take the ride I just mentioned: Overdoing it once kept me from riding for a good 3-4 weeks, because the tendonitis in my knee was really really bad.

Maybe I am just getting old and stuff, but my back issue and stuff like the knees knocked loads of confidence out of me in that respect. For me, overdoing it seems to come at a price that is detrimental for the overall progress of fitness and ability these days, if you know what I mean?

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?