Well, I certainly wouldn't rule out arthritis either. I'm 27 and have suffered with arthritis in my hips and knees for about eight or nine years now. It's very common among riders (here anyway), especially in the right hip (since that's doing the most work when you mount and dismount). Of course, I also had five rather bad falls in a short space of time - because when the doctor told me to take four to six months off riding I told him to shove it (not quite so politely). So I guess that's possibly accounting for the constant back pain and regular headaches. Ibuprofin and cataflam are now my very best friends. They're cheaper than going to the chiro or physio, not that either of those therapists can do much for arthritis.
It is not 'cool' to ride without a helmet! period.