YASID human biological age frozen short story

This is a short story in a _The Year's Best Science Fiction_ volume.
Takes place in a world where some event caused everyone's body to stop
aging and developing in most ways. So while a nine year old girl
(which the main character is, if I remember correctly) becomes more
sophisticated intellectually, she does not grow any taller, age, go
through puberty. The main character is in real estate and lives in
what is essentially a play house with several similar "age" friends.

--
Phillip