I suppose it depends on a lot of things - how much fluid you have in there and the position and size of the baby and the position of the placenta. As they get bigger you can definately feel and see it from the outside. With this pg I had been feeling movement for about 6 weeks before I could feel it properly from the outside, so about 17-18wks for me (but this is my 4th so the tummy aint so taught anymore LOL) and now the kids can even see the movements when he is really getting into it.

Oh, I just noticed we are due on the same day too - so don't worry too much about what I've said and it won't be long before you can feel bubs kicking away.