Almost two-thirds of New Yorkers arrested for firearm-related murder and attempted murder charges are 25 or younger, according to data requested by amNewYork from the New York State Division of Criminal Justice Services.

From 2009 to 2013, about 62.8% of those booked on murder or attempted murder charges -- with an underlying firearm charge -- are 13 to 25 years old, according to the data.

The data included only those charged as adults

At a young age people's brains aren't fully developed and are succeptable to negative influence, said Dr. Judith Ryder, an associate professor of sociology and anthropology at St. John's University.

"If you add in guns what might have been a fight can turn into a homicide very quickly. And kids have access," Ryder said. "They are lacking in impulse control."

"You place on top of that all these stresses of a neighborhood that is missing so many things, that contributes to it," she added. "Kids do stupid things, but if you have a gun in your hand it just makes everything so much worse."

The pervasiveness of this problem comes down to a dynamic that has plagued the country for decades: not enough after-school activities to keep kids occupied , said said Joseph Giacalone, a retired NYPD detective who now lectures at John Jay College of Criminal Justice.

Last year there were 259 people arrested on firearm-related murder and attempted murder charges and about 59% of them were 13 to 25 years old, according to the New York State Division of Criminal Justice Services. That number spiked to about 69% in 2012.

"There is no doubt about it you have more kids out there being unsupervised," Giacalone said. "We need to reach out into those communities and fix the problems where they really are: the families."

"If you don't have those social attachments... there's a good possibility that a kid will turn to crime because he got caught up with the wrong group," he added. "Many of these kids, they follow the cool kids and they want to belong."

The NYPD and the mayor's office did not respond to several phone calls and e-mails requesting comment for this story.