I am a 28 year old female and think I may have arthritis in my knees and neck. Is it normal to get arthritis at this age? I use to do gymnastics also.

Not really. It is early to get osteoarthritis to a great degree in a 28 year old, particularly in the neck. It may be related in part to your prior gymnastic activities and possible injuries that occurred during that time. I would not hesitate to be seen for a specific diagnosis and treatment options.