The fastest-growing population to try marijuana these days is not rebellious teenagers. Guess again. New research from the National Survey on Drug Use and Health, an annual federal report that began over 50 years ago to provide up-to-date data on the use of tobacco, alcohol and illicit drugs as well as mental health in the United States, has a very different finding. Instead, it’s people age 65 and older who are experimenting with marijuana more than any other age group.