Obviously the Iris in the B2/W2 games is different than Iris from the Anime. Not even close and able to compare them. Those are two different things.
Why would it be impossible for a kid to be the Champion??? The characters in ANY Pokemon game are depicted as ''kids'', and you have to defeat the Champion in each game, that would technically make you, a kid, the new Champion.
Therefore, Blue, Red and so on were kids also. And Bue was a Gym leader/ Champion and about the same age as you so that's possible too. Or Bugsy, a pretty young Gym Leader as well. I can't see why it is impossible for a kid to be the Champion.
Sure, the games have SOME slight resemblances towards the anime, but they are still two seperate things. Like said earlier, they changed some things in the games compared to the anime. Not any Pokemon game is entirely the same as the anime, so this is from all times.