a year old

Raffles

You can change now. I started my cat Isis out at 5 months of age and she did
just fine with adult cat food.

Depending on activity level and breed, 6 months to a year.
Kitten food has more fat and calories for growing kittens (and pregnant or
lactating queens). It's calorie-dense, so that they get more when they don't
eat a lot. They'd have to eat more, quantity-wise, adult food to get the same
amount of fat and calories and many kittens won't eat enough due to their
small tummies. Some eat quite enough, even too much, so when free-fed, they
get fat. If your kitten is already above the weight he/she should be, you can
switch now.
If your cat is one of the larger breeds (over 15 pounds expected normal
weight at maturity), such as a Maine Coon or Norweigen (sp?) Forest Cat, wait
until a year of age to switch.

For my garden-variety DSH's, I switched at about 7-8 months.