[Professor Geoffrey]

I don't really see any "growing up" features. In Pokemon 3, the Lord of the Unown tower's Piakchu mini-movie, Ash, Brock, and Misty were making a party, parcially because that was the day Pikachu and Ash met. My guess of his age would be... Well, when the Manaphy movie comes out, I'd guess about 13. And you wondered how I got to that conclusion...