What evidence is there that Jem is growing up?

Incomplete question. I assumed you are referring to Jem, a character in the novel, To Kill a Mockingbird by Harper Lee.

Explanation:

Recall, that unlike Jem's actions or tolerance level changed during the course of the story. For example, Jem no longer feels interested in playing the usual games he and Scout played before; indicating mental growth.

Also, we could notice that Jem consumes more food than previously consumed by him before; a sign indicating he is growing physically.

this would be in the imperative mood. it is a category of verb forms that are used to express orders,instructions,commands or requests.