Well, it took three weeks for my 4-year-old to not growl, or run away, or run away growling. He did rush an attack a couple of times, but the 6 month old kitten handled it beautifully with appropriate responses, and I scolded Simon with some "No's". Eventually, they blended and Simon and Noah run around together and generally get along, except for the occasional possessiveness of owner syndrome. It is more difficult with older cats perhaps, but nobody is going anywhere and time can be your friend.