When should I start crate training my puppy?
The sooner the better! Crate training should first start as an engaging activity (snuffling, hiding food, hiding toys inside) to get your pup feeling curious and interested in spending time there.
Furthermore make sure that your pup's crate is something they get to access when they're tired. Once your pup is comfortable being in and around your crate without it being closed, you can keep it closed while they're not inside, so that you open it only when they're feeling tired/in need of rest.
Saving the crate for when they're actually tired will help create that association and interest in the crate, as it will feel even more special, and just right!