I am confused about Penny saying to Piper when you were this age and we had the witch talk. I thought they were adolescents or younger when their powers were bound, while this spell they seem to be teens.
Edit
At the finale {forever charmed} it was revealed that Grams talk to little Piper and her sisters in code, telling them how special they were and one day they would find out how gifted they are.
It's also implied the Halliwells understood those conversations when they became witches.