Here is a cool photo by Reddit.com user: u/daantjhuu. This cat looks like a Maine Coon although the photographer and owner does not tell us. I love these before and after montages.

If this cat is a Maine Coon he/she is not fully developed as those in the know say that this cats of this breed are slow developers. They reach adulthood at around the age of four. But perhaps they reach their maximum size before then. This page might interest you: When do domestic cat stop growing?
I have a page on life stages, which also might interest you – please click here.
SOME MORE ON MAINE COON KITTENS: