Osteoarthritis is degeneration of a joint. It is a non-inflammatory arthritis as opposed to rheumatoid arthritis, which is an inflammatory arthritis. Osteoarthritis typically occurs and worsens with age. However, early onset osteoarthritis is possible if there is a history of trauma.
Not only can trauma result in early onset osteoarthritis, osteoarthritis can also be caused by other health conditions. It can result from obesity or simply natural degeneration and wear and tear.