HugoDane

I have a 11 week old male great Dane, I was just informed by the vet that he has 1 testicle and the other may be in his scrotum or abdomen. He states that he will need to be castrated at 6 months. Does it have to be done at 6 mths or can you wait till 12mths. I'm only concerned as I was told that castrating early can hinder the growth stage. The platelets stay open which leads to skinnier lankier dogs. Any info would be much appreciated.. Thank you