Is it bad to be double jointed? will i have arthritis before old age?

Not bad: "double-jointed" usually refers to a degree of natural ligamentous laxity. There is no evidence to suggest that you are at greater risk of getting arthritis. This laxity does have implications in certain other processes, such as shoulder dislocation/pain. In the absence of a particular complaint, it is not bad. Interestingly, being double jointed is common in elite athletes, so maybe it is good.

No such thing: There is not such thing as being double jointed. What this describes are people who have more mobility in there joints that the average population. This can be genetic and be associated with a condition called marfans. This hypermobilty can lead to injuries of the joints which can lead to arthritis down the road in some people. Talk with your doctor about it.