I had an anterior placenta with this pregnancy. I felt some small movements very early on, but they weren't regular (this is my 3rd baby, though, and I felt the other two early as well). At 16 weeks I was feeling some movements at least once a day. The movements were still small, but I could count on feeling *something* daily. After that, I did have a few days where I got worried because I couldn't feel her move as much, and at 17 weeks my midwife had a tricky time finding her heartbeat with the doppler. She had found it easily at 12 weeks, but the baby had moved out of my pelvis after that and... and had more room to dance around and escape in my belly area. Lol
The midwife suggested that the sporadic movements may have something to do with an anterior placenta. I'd never had one before, so this was all new to me. At my 19-week scan they discovered that I did have an anterior placenta. I was still feeling movements, though... I would just feel them around the area that the placenta took up, instead of right in front. I had another scan at 23 weeks and they didn't mention the placenta. By 24 weeks I was noticing that I felt movements all over (not just the bottom and sides of my belly like before). At my 25 week appointment, I mentioned to my midwife that the baby must be getting stronger because I could feel her even in front through the placenta now... And she said that, according to my paperwork, my last ultrasound showed I no longer had an anterior placenta. Go figure! Apparently my placenta had moved up into a fundal position (top of the uterus) and that's why the movements suddenly felt stronger. So weird!
At any rate, I'm almost 26 weeks now and the baby was kicking super hard yesterday. She was popping my hands up as I rested them on the top of my belly. LOL. I think it varies so much for everyone, though. There are some women who (even with placentas not in the anterior position) don't feel much from their babies until like 24 weeks.