Fannie Hamilton sat among teenagers during the Sunday service. She used her left hand to hold up her stroke-affected right hand in praise, belting out the words to "My Glorious" by Delirious. A few minutes later, she stood next to a 16-year-old, who joined her in belting out the words to "Great Is Thy Faithfulness." She was a small group leader in our youth ministry—at the age of 82.

She embodied my vision for the church as real and relevant to all ages. I had envisioned a church with young and old and in-between learning from one another, deferring, serving, praying, working, worshiping together—one heart, one mind, one church (Acts 4:32).

I long for a church where teenagers don't leave as soon as they turn 18. According to George Barna, there are 8 million teens active in student ministries now but who will no longer attend church when they're 30—a 58 percent drop in church attendance during the 20-something years. That shouldn't be.

In my 12 years as a youth pastor, we equipped ...