My Grandson Is 9 Yrs. And Still Love To Wear

My grandson is 9 yrs. and still love to wear his mum's shoes, fancy clothes (dresses up with girl cousins of his ago) and my son is unable to understand why he does this. This has been so since he was a very young boy. He plays only with girls at school and has no interest in sports, or other "boy" things. I believe my Son should talk to a psychologist and learn how to react to this unusual behaviour.