Is having tendonitis at a young age abnormal and how long until it goes away?

Tendinitis : Tendinitis is common with injuries, overuse, and many arthritis diseases. It is most commonly discussed as a part of a class of diseases called seronegative spondyloarthropathies but is also associated with other inflammatory and non inflammatory forms of arthritis as well as many developmental and structural problem unless the cause is obvious it would be best to discuss this with your doctor.