My 6 year old son still walks on his tiptoes. Will he outgrow this?

Must be seen. I think it's time for your son to be seen by a Pediatric Orthopedist. I think it's too long for him to be walking on his tiptoes, and I'd recommend an evaluation at this point.
See below. Toe walking at his age could be associated with tight heel cord, cerebral palsy, or weakness of proximal muscle group. I would have him checked by neurologist.