Movement can be felt around 16-18 weeks from a vigorous baby, later if the baby is a bit more sedentary. Some are stronger than others. Some are larger than others.
The first perceptible movement is a little fluttering; the baby is not strong enough or big enough to actually push on the uterine wall, she only kind of touches and bounces off it. Later, as they can brace themselves against the other side of the uterus, things get quite a bit more dramatic.