Once upon a time, boys and girls grew up and set aside childish things. Nowadays, moms and dads skateboard alongside their kids and download the latest pop-song ringtones. Captains of industry pose for the cover of BusinessWeek holding Super Soakers. The average age of video game players is twenty-nine and rising. Top chefs develop recipes for Easy-Bake Ovens. Disney World is the world s top adult vacation destination (that s adults without kids). And young people delay marriage and childbirth longer than ever in part to keep family obligations from interfering with their fun fun fun....