After a little searching, I found out that St. Maria Goretti was the youngest saint of the RCC (and not St. Dominic Savio as I thought for a while). The Friends of St. Maria Goretti site is a nice place to look around for more info on her. Incidentally, St. Dominic Savio is the youngest non-martyr saint (St. Agnes was 12 when she was martyred by the Romans).