It all started for me in 2002 with Cagalli Yula Athha from Mobile Suit Gundam SEED.
Now remember kids anime was a diffrent animal back then and lolis as we know them today where not really around yet. Any who it was then that i really started to notice i perferd the smaller / flater chested girls to the more common big brested ones.
Since then lolis have become more main stream and changed the way they look as well. They use to be taller (still shorter then the rest but taller then now) but smaller chested. Even has late as recent as 2006 this was still considered a loli:
Kaguya from code geass