You may well find it a lot harder to get him used to the kennel at 6 month old after being kept in the house. To me that would be a bigger shock to the system. Do you have any other dogs outside in the kennels already?
You are going to be faced with that many opinions that it wont really help at all, but personally I would have him outside immediately. Bring him into the house when it suits but back out at night to 'his' space. You are also reaffirming that you are in charge and its up to you when he gets his freedom. May sound daft but its all part of the pecking order being established, especially if you have kids or a wife who is just going to spoil him regardless!
Its 10deg here today, that is not cold providing its out of any breeze in a well built wooden kennel for a lab pup. The acclimatising by being outside will stand him well for working in all conditions in the future and ensure a good casting and re-growth of coat in the different seasons...