First, welcome to the forum and I am sorry that you are hurting.
Hmm... your age alone does not rule out or rule in arthritis. On and off pain in a knee and an elbow also doesn't rule in or out. Can you be more specific as to when it hurts for how long what you were doing when it started hurting...
Also, other symptoms - are the joints hot to the touch, inflamed, are you fatigued, stiff in the mornings, does the pain or stiffness go away as you "warm up"
Sorry I cant be more helpful but I think you will get better responses as you supply more info.
And of cource we aren't doctors and can't diagnos you but we can offer advice and support.