My grandson wasn't circumcised after he was born. he is six months old now shouldn't i be able to pull his skin back to clean him?

No: Do not pull the foreskin back on this 6 month old male, you may damage the penis. You need to allow the male boy to reach age 5 before pulling back on the foreskin.

Leave him alone: As long as he has enough room for the pee to get out he's okay. You can gently wash the area with thin soapy water & tease the foreskin back a little to get at any accumulated debris but otherwise leave it alone.As he gets older & starts to bathe himself, he can be taught to gradually coax it back.By 5 or so, most will release naturally.Forcing it too soon can cause a firm skin adhesion to form.