The thing with kids - is that all of this happens so quietly, you don't even realize as they start to do new things. Ok, crawling, walking, talking - those type of things you tend to notice. But it's at the age he is now that these new things are happening every day. And it's not until you kind of stop and think about it and realize - hey, this is new. He's never done this before.
And then of course, if you are me, you take pictures and video tape it.