There really is no age, it's all about if you have good posture, or if you use your back to lift things, or do you work somewhere that strains your back? (I have that problem)
I thought that too, believe me. Join me in looking for a good chiropractor everywhere you go and praying that this doesn't mean you'll end up paralyzed by 40.
I actually have better posture than most of my classmates, I don't generally lift things at all, and I'm a lazy b*tch who has no job (not for lack of trying, mind). ._.
I'm younger than you, only a year, but I started having back pains maybe two years ago. I'm pretty top heavy, and my poor posture helps not.