I have had arthritis since my early teens. It is not confined to the elderly. Some people have hereditary tendencies to arthritis. I definitely have.
Try to stop clicking your fingers. My son did it and was told by the doctor he was likely to get arthritis because of this habit. Apparently, it's more common in boys than girls. Any joint that is overstretched is more prone to arthritis. Fingers are not meant to be clicked!
I wouldn't worry about it though, but when and if you have a GP appointment I would mention it.