jaka, I don't think it really matter if they full bread or half breed, I think it happens at roughly the same age. I don't know about dogs but cats need to be neutered at the age of six months so it is probably the same for dogs but don't quote me on that. Your best bet is to call a vet and get some advice or read some books. Another suggestion is to go up to Dog General and ask there as someone might be a bit more experienced there.

Good Luck!