A prominent member of the JFK research community once denied to me the plausibility that Oswald could have been a juvenile informant on the basis that no agency or police service would ever use juveniles.
This is from the National Criminal Justice Reference Service (emphasis mine):
The majority of law enforcement agencies are unlikely to have established policy for the use of underage informants, most are reluctant to officially admit to the practice. However, emphasis on drug arrests and the continued use of illegal substances by teenagers increases pressure on law enforcement agents to engage juvenile informants. Information provided by juveniles is useful to police officers, but the role of an investigative informant places the youth in danger. Additional research is recommended that can inform policy and police procedures is needed to fully understand the dynamics of juvenile informant situations from a variety of perspectives. Police use of underage informants presents many of the same problems that have been documented in regard to adult informants. This article examines emergent trends, noting some of the lethal consequences for youths who have taken on the role of police informant through case presentations. The views of law enforcement personnel regarding their involvement with young people in undercover work is presented, as well as details of legislative responses to the use of underage informants. The exploratory research was based on interviews with 21 law enforcement agents in a large city.
It is not just police who use them.
Wershe was recruited by the FBI at age 14 to join the fight in the war on drugs as a paid confidential informant. He had no prior involvement with drugs. He was selected for informant recruitment because he knew and was trusted by a neighborhood black family targeted for investigation as suspected cocaine traffickers.
Other agencies known to use them included the Treasury Dept, countless privately run intelligence/counterintelligence groups, housing estates, and federal, state and city committees and ad hoc investigative bodies.
The idea that Oswald was recruited as an informant during his time in NYC is therefore far from "far-fetched". His period of truancy began when he turned 13 and ended when John Pic left the Port Security Unit.
And as shown in Volume 2 of Lee Harvey Oswald's Cold War, Oswald was most likely recruited into counter-intelligence work at age 15 by David Ferrie through his internal CAP group