My tinnitus started despite being young and having subjected myself to far fewer loud noises, including concerts, than the average person. My doctor believes that mine is likely due to a neurological issue, but that we will never know the true cause. To satisfy our own curiosity (and determine if we could attempt to treat it with steroids, which is possible during the few weeks after the onset of tinnitus induced by hearing loss), we had my hearing tested. As expected, absolutely no hearing loss.
As others have said, I felt suicidal during those first few weeks. Thankfully, I've since learned to live with it.