To be totally honest theres no set rule.Some have my pups have had a quick blast and chase in the rabbit pen to gee then up a bit.. others aint allowed to see anything as they are too hot to begin with and the last thing they want is more excitement,so to try and answer your question truthly ......theres no set answer..theres simply too many variances..but ill have a go
Depends on the dog and depends what you mean introducing to game ...Six months is ok in a contolled situation..Retrieving a dead partridge or rabbit .. rabbit skin dummy but six months is way too young to be attempted to shoo