training older dogs

Can an experienced trainer advise me please..is it possible to train a three year old dog to a good level to hunt (deer) and retrieve ?

First thing, a three year old what?

If it's a terrier you may never be able to train it, it may never have been trainable anyway, but if say it's a three year old dog from good working lines it will most certainly be trainable to some extent, that extent being determined by the extent to which it has been f***** up by the original owner/owners.