its definatly possible especially if you are still gaining hieght.. if its growing pain its generally right above the joints accociated with the long bones of the body... like the femur or humorus ... if the pain is sharp it could be something else.. and it is uncommon for someone your age to get them because the majorit of fast growth is done and the rest of the growth is a slower process.. do you have the pain all the time? or during certain activies or just on and off?
21 year is the time you stop growing so I guess it may be possible , may I ask where the pains are you gave very little information ..
it all depends on what type of pain