Wait until a big doe with young latches in to its nose or under its eye and see how much drive your 3/4 month old puppy has then?
No one ever spoilt a dog by entering it too late but many, many been spoilt by entering them too early.
There's no great rush mate, rats will still be about when it gets its second gob? by all means let it hunt and learn but I certainly wouldn't push it.
Cheers, D.