ive known borders to go at 12mts, i find that each and every one is different, some take longer to go, but if i was you i wouldnt try them at 8mts far to young, if they meet summut it could put them off for good,you say you have just got them, get to no them and them to no you, take um out bushing and all that, maybe let them watch a dig or 2 in afew months time, and dont for get to put a collar on, as has been said there just pups , if you dont mind me asking why did you choose borders,