I have an AP and started feeling her move at 15 weeks and did ever since. I think it really depends on where the placenta is and how sensitive you are to baby's movements, but that's just my opinion. It probably plays a factor that this is my second pregnancy. But a lot of women don't feel baby move till 20 weeks or later regardless of placenta placement. (: I'm sure your dr was just letting you know you might not feel baby this early so you don't start to worry.
I also have anterior placenta but i felt my baby kick starting at 16 weeks, you may still be a bit early to really distinguish wat u are feeling but give it like 2-3 more weeks you will def know for sure the feeling will be more noticeable.