User blog comment:Zathronas/Speculative author: The Grimm and the next season/@comment-78.42.186.25-20141011171528/@comment-7622429-20141011190047

The older they live, the bigger, more powerful, and more intelligent and experienced they become. Basically, if you let them live long enough, they'll just keep on growing both mentally and physically. There's no apparent "growth stop" as we know yet.