While other kids were shooting hoops after school, 16-year-old Isaacman was building a multimillion-dollar debit-card processing firm in his parents' basement. Now 23, Isaacman provides ATM services to nearly 40,000 clients, including Burger King, Ferrari, and other corporate VIPs.

Age: 23
Location: Hampton, N.J.
Revenue: $58 million
Employees: 138