At 36, he is a counselor for an ex-offenders’ advocacy group. The arc of his life traced what criminologists have long recognized as a pattern of aging out of lawlessness. The most criminally active -males between the ages of 15 and 29-usually lose their enthusiasm for crime as they belatedly mature in their 80s. So experts had been hopeful that, as the nation’s population aged, crime would decrease into the early 21st century.

Now meet John G., 17, the American-born only son of a French-Caribbean family of seven living, off and on public assistance, in New York. A dropout who could hardly read, John often clashed with his abusive, itinerant father. Two years ago, street-hardened and gunslinging, John robbed a middle-aged man on a Brooklyn street, sending his victim to the hospital. Given a five-year sentence, he is now on probation. He reflects the new younger, tougher face of crime. Young criminals have traditionally been less violent, specializing in crimes against property, but the current trend is toward younger violent felons like John G. This has many criminologists believing that the future benefits of large numbers of older criminals aging out of crime will be offset by smaller numbers of younger, but more menacing criminals. “You’d better fasten your seat belts,” says James Fox, a professor of criminology at Northeastern University, who says the country is in for a violent crime wave as the number of teenagers increases by 23 percent over the next decade.

It’s happening already. Todd Clear, a professor of criminology at Rutgers University, notes that while the proportion of 15- to 29-year-olds has been falling since 1980, overall crime rates have not fallen as rapidly as during similar drop-offs in the past. “What you’ve got is the younger age group contributing more than their fair share,” he says. From 1965 to 1990 juvenile murder arrests alone rose 332 percent. In 1969, when 15- to 29-year-olds made up 24 percent of the population, the violent-crime rate (homicide, rape, aggravated assualt, robbery) was 329 for every 100,000 people. Twenty years later, when that age group shrank back to 24 percent, the violent-crime rate more than doubled to 663. The trend is likely to continue, driven by deepening child poverty, destabilization of families and more guns, drugs and nihilism among young people.

Eventually, even the John G.s will age out of crime like the Jose Vasquezes. But the wait is likely to be longer and more harrowing. And then come their children.