What age group gets arthritis?

I dont know how old this question is, but I decided to answer it anyways. Arthritis can affect a person at any age, usually it is older people who have this problem, but you can also be born with it. I have a friend who is 21, and she's had it her whole life, being born with it caused her to have bent joints, and very small bones. She also has smaller features, because of this. She takes many meds, and has appointments every year to check her well-being. :)