mate the earlier the better! start on a sucker at about 3 or 4 months and you'll find you'll have a handy dog at about 18 months, i got an 18 month old bitch i started that early and now she's cracking, works off back off ute no worries
mate i run anything that'll have a go. got a real handy bith that's staghoung/harlequin dane, only thing is she's deaf but wat she lacks in hearing she makes up in the nose department. got a litter of pups on the way with the father beig mastiff/dane x bull terrior/red cattle dog and the mother border colliie/kelpie. be interesting to see how they go