POGO,
Don't worry yourself over those who doubt. This is the internet, home of the skeptics.

I think being able to share an interest like this with your son is wonderful, regardless of what skill level he achieves.
Anecdotal moment: my own son is only a month older than minipogo. While he does not have any interest in Go (since I don't actually own a board, he doesn't see me playing at all), he has an attention span for some things that would easily allow for playing a full 19x19 game of Go. In addition, he has an interest in patterns that would also be helpful. I don't have the time to see if he could learn, but I suspect he could, if I had a board to play on with him. I'm constantly amazed at how quickly he grasps things, and he spends time thinking before acting more often than I would have believed before I became a parent.
Back to minipogo, it would be wonderful to see him grow up and maintain interest in the game. The skeptic in me holds a "wait and see" attitude ... time will reveal everything, and really I'm just going to enjoy watching things progress regardlss of the outcome.
Keep letting us know how minipogo is progressing, POGO!
- Marcus