I felt it from about 15 weeks but it was very much fluttering and a kind of soft dragging with the odd nudge rather than the full blown belting kicks that I'm getting at 21 weeks! Don't worry if you can't feel anything until after 20 weeks though, there are all sorts of reasons you might not be able to feel them until later.
I'm 16+5 and have had 'bubbles' for a couple of weeks, but yesterday started getting the very strange sensation of being poked in the belly from the inside! I've never felt anything like it before, but it's happened a few times since and always in roughly the same place. Having said that, the 16+5 is entirely based on my dates, my consultant did my 'dating scan' which lasted all of about 20 seconds and no measurements were done, so it may be I'm a little further on, who knows!