Well, I'm only 21 so I know what you're thinking... but I've had a bad back for no lie, 8 or 9 years now. Basically destroyed it one morning have batting practice at 7 a.m. without stretching or anything... about 4 years ago I got all these tests done and they found I had Spondylolysis; aka pars defect; aka stress fracture in the lower back which causes your discs and vertebretes to be unbalanced and such. My back is still in really really rough shape... can't play sports without having to take a break to rest it/stretch it out... cannot run on a hard surface for an extended period of time (I used to run like 4 miles a day... now i can't eve finish a mile)... but the one thing that has never bothered it has been rides... not any rides... the only ride that somewhat does actually is dinosaur... since its jerking you around and such... I've never had a problem with rollercoasters though... just my 2 cents