So when, exactly, does adolescence start? The message to send your kid is: Everybody's different. There are early bloomers, late arrivers, speedy developers, and slow-but-steady growers. In other words, there's a wide range of what's considered normal. But it's important to make a (somewhat artificial) distinction between puberty and adolescence. Most of us think of puberty as the development of adult sexual characteristics: breasts, menstrual periods, pubic hair, and facial hair. These are...