Both my 20 pounder and my 13 pounder continued to grow after one year. Cookie went from 9 pounds to 13 pounds in her second year (although some of that is tubbs - she's now on a diet!) Her vet said she should weigh about 12, which is way above average for a girl. Big was a whopping 8 pounds at 4 months, which is twice average, was 15 pounds at 1 year, and at 2 is now 20 pounds. He's on a diet, too! But, like his sister, even after he loses enough weight to make his doctor happy, he will still be about 17-18 pounds. So they clearly continued to grow past their first birthdays.

Although they are not 100%, they appear to have Manx blood, which is a large breed like Maine Coons.

Back in the 80's a coworker raised Maine Coons and she did once tell my they generally achieve full size at about age two.

Most other breeds are considered full grown at a year.