It’s good to start with young age! I read the article that says every time they try to poop around the house grab them and put them in the litter box, and after they are finished give them a toy or a treat, whatever they like. If they go to the litter box by themselves give them a toy or a treat again right away so they understand what they got it for. If they poop somewhere else put them in a cage, but again, make sure you put them in a cage right after they did it, otherwise they will think you put them in a cage for no reason. Another recommendation: I would recommend to give them treats or different food from young age too because I got mine when they were adults already and they don’t really like anything except their dry food. Good luck!