it will take some time no matter what the age. if the picking on goes on for more than a day then i would think about seperating. i have 4wk olds, with 3 week olds, and 2 weeks olds. they took some getting used to each other in the beginning, but now everyone is happy as can be. the yougest ones look like the little brother and sisters trying to keep up with the scratching of the others, its kinda cute