What might Jem's age have to do with his reaction to the verdict?

Jem cried over the verdict. Jem is now 13 years old and understanding the darkness of human nature and the unfairness of the world. He sees, in particular, how bigoted and unjust his friends and neighbors are. Jem has matured a lot since the beginning of the book. He is leaving his childhood sense of wonder and security into a world that is not always fair and just.