I think Abby (Chi x) hit 15 months - ish and just matured. She has always been just a little bit serious in her personality. She still loves playing, but she is so steady and serious the rest of the time. And there is a pretty clear line between playing and the rest of her approach to life lol.
Gracie (stafford) is 11 years old and to be honest the line is not clear at all. Her whole life is a game. I still can't cut her nails in one go without fits of laughter and a whole lot of effort (my fault, never bothered to train it) - she doesn't sit still and thinks it's a game. Not very mature and doesn't look like she's going to bother with it now. Not a day goes by where she doesn't do something dorky.