the youngest I had mine was 6 weeks, but, it was smooth going from day one(she was 1 or 2 days shy of 7 weeks)..Infact, I started working with her pee pad training right away, and 2 weeks later when I hauled her all the way to Illinois with me, she was already running to the pee pad..of course, she was a good eater, and I had already had a maltese with hypoglycemia, so knew what to look for |