My son Ace is eight months old. We started pricking his heel ony once a week when he was around five months. We rotate (Left heel inside one week, and then right heel inside, then left outside, and then right outside) so there is never usually a scar. Also, the PA Department of Health supplies us with tenderfoots which is like a little plastic box and the needle is spring loaded so it is pretty easy to do and makes a clean prick. Is that what you are using?
I have heard that most people switch to the finger at a year also?