Do you mean physically mature late like bulls (up to 2yrs), or mentally late developers.?
What do you pay most importance too, physically or mentally developed when bringing a pup on? For me the pup would need to be both physically and mentally ready.The softly, softly approach. Just seems to me that theres alot of people on here letting their pups go on rabbits at an age I would never dream of doing. I can see alot of dogs being ruined imo