West Memphis Three
At the time of their arrests, Jessie Misskelley, Jr. was 17 years old, Jason Baldwin was 16 years old, and Damien Echols was 18 years old.
Three Investigators
For the original series, the specific ages of the investigators were never revealed, but contextual information indicates that they were likely 13 or 14 years old. They were not old enough to drive a car legally, but were said to be just a few years younger than their nemesis Skinny Norris, who had a driver's license from a state where the required age for a license was younger. On one occasion it was mentioned that Pete was part of the high-school wrestling team. In the later Crimebusters series, it was stated once that the Three Investigators team was initiated when the boys were 13.