hey i had the same queation 2 months ago as my female golden retriever was in heat and i thought her to be mated with my male golden retriever but my vet said no for it . He said at this time if my male retriever mates a female dog there will be some hormonial disbalance. . He said dont let him mate until and unless he is 1 year old. . I got my female dog mated with a champion golden retrieverafter that. .I paid 20k extra even when i had a male dog so, i would ask you to not let him mate until and unless he is a year old. .