Girls that Grow?

[Magicflier]

When I read your description, the first thing that came to my mind was Mahou Sensei Negima!, though only manga-wise sadly.. the anime barely follows the manga.

Saki fits your description pretty well, so does:
Binbou Shimai Monogatari
Da Capo II (though the focus is more to the sad parts though, before she grows..)
Eiyuu Densetsu: Sora no Kiseki (not sure about the anime's genre though)

Hope these might fit your description?

[Magicflier]

I've forgot to mention Kimi ga Nozomu Eien, this anime is possible