When I wrote my book "Discipleship Matters" God led me to aim it at young men. And indeed it has worked well with that demographic. Since publication I have led numerous young men through the book and it has been a rewarding experience. Dr. Robby Gallaty says it is probable that the Twelve Apostles were teenagers. His seven reasons are as follows:

Jesus used Greek words that suggest the disciples were young. See Matthew 10:42 "little ones" (mikros) and John 13:33 "little children" (teknion).
According to the Mishna, Jewish boys were schooled on a particular schedule. During their teen years of education it would have been more likely for them to go follow a Rabbi.
Marital status. The only disciple we know who was married was Peter. Jesus healed his mother-in-law. The others were probably not married because they were under the age of eighteen.
The Temple Tax is mentioned in Matthew 17:24. Exodus 30 says every Jewish man twenty years of age and older had to pay the Temple Tax. The only disciple who had to pay the tax was Peter.
Traveling. It would have been highly unlikedly for married men to leave their families and follow Jesus. It would have been easier for teenagers.
Longevity. Based on the dating of the book of Revelation, we know John lived until the late first century, therefore he must have been young when Jesus called him.
Immaturity. The disciples being young and immature were unable to understand theological concepts, unaware that a devil was among them, willing to call down fire from heaven on their enemies, argued about greatness, and put their mother up to ask the Master for preferred seating.

Mark Clifton has written "Reclaiming Glory: Revitalizing Dying Churches." Mark is widely seen as an expert in the field of church revitalization. In his book he mentions six imperatives for congregational renewal, one of which is focus on reaching young men. He properly notes that a dying church never says, "We have too many young men around here. We need to attract some older adults." But obviously all of us in church work have seen the opposite.

How fascinating. Jesus reached young men and Clifton says young men are the key to church revitalization. I know where I want to keep spending my time and energy. How about you?