I'm 16 years old, just started cycling half-hour each day about a week or so ago. After a couple of days however, there's been a bit of a problem, with my lower back hurting. It doesn't really hurt while I ride (just a little twinging maybe), and today, I stretched real good and it didn't hurt straight away when I got back from my ride, but then when I sit down at the computer for a while, it starts up again.
Either A) My seat or handlebars are too low.
or B) I'm not used to working those muscles.
I can see the physical benefits. I had slight love-handles which are disappearing slowly I think (there's definitely a change in my lower back area). Torso-wise, I'm quite a small guy, but I have a curvy butt (not to mention quite big legs - not fat, just big), and I envy those whose backs just go straight up-and-down, so that's what I'm trying to do - improve that area a bit.