Gene feels power when he trains with Finny.
He begins to push himself further and further until he is able to go well past what he was once able to do.
B. Overgeneralization
They are saying that "practically every teen cares" but have no real evidence to back that up. They may have polled a small group of teenagers and because the majority of them said they care about animals they generalized that information to represent everyone in the age group. Without a full poll or teens there is no way to know how many do or do not care about the welfare of animals.
