Any suggestions for a teenager thinking of the priesthood?

A woman in my parish dropped me a line today:

I’d like your advice. The other day a young man, still a boy, told me he was thinking about becoming a priest.  I was very touched by the fact that he shared this with me. I’ll pray that God guides him until he reaches a decision. For Christmas, I’d like to give him a book that tells the story about a man going through the process of discernment, if there is such a book. I read your post about (Thomas) Merton. Would this be a good example?  I thought about biography of saint, but not all saints are priests. Kindly recommend something appropriate for his age (about 15 years old).  Thank you!

I think “The Seven Storey Mountain” may be a bit much for a 15-year-old.  Any ideas?  I’ll happily pass them along …!