When should I begin to use a kennel? When he is a puppy? Or later on?

I'm a cat person, and have never had a dog, but have learned by reading threads here on this site that a cage or kennel is supposed to be a dog's "safe place," not a place of punishment. The dog should not be locked in a kennel all day, and a puppy especially has to be trained to it carefully and gradually.

Read through appropriate threads on this site, and a dog expert will be along to answer this more thoroughly than I did.

Use one as soon as possible.

If you allow the puppy to sleep on your bed or even locked n a certain room of the house with his own bed it will be a lot harder to crate train him later.

I made that mistake with my puppy. When I first got him he was already crate trained so we continued crating from the day he arrived.
Well, winter came and it was cold in the bedroom (he's a hairless dog) and we let him on the bed with us.
4 months later he's still on the bed with us and whines and cries when we try and crate him.

If you are consistent, and the pup learns what is expected of him (ie: being quiet in the crate) he will continue to be good.
Dogs, like children need consistency and structure in their lives, if something changes, no matter how small, you can expect changes in behaviour.

If you need any crate training tips just let us know and we'll be happy to give a few pointers.

You should start kennel training as soon as you have your puppy. You don't need to wait for a certain age.