That's according to a new study published Monday in the Annals of Neurology. The study was done by the VA Boston Healthcare System and Boston University's school of medicine.

The study found that among 211 players who were diagnosed with CTE after death, those who played tackle football before age 12 suffered from cognitive, behavioral and mood symptoms earlier than those players who didn't start to play until after age 12.

Every year a player played tackle football under that age predicted the early onset of cognitive problems by 2.4 years, and behavioral and mood problems by 2.5 years, according to the study.

The study included 246 former players, 211 of whom were diagnosed with CTE after death.

Dr. Ann McKee, director of Boston University's Chronic Traumatic Encephalopathy Center, appearing on ESPN's "Outside the Lines" Monday, said the findings indicate those who play football after age 12 show more resilience against brain disease later in life.

"It shows the health of the brain was changed by playing football before the age of 12," McKee said.

"Some argue that players should play even later than 12, maybe 18, when they are adults and can make fully informed decisions," McKee said. She added that players who are older have more mature bodies and might be more capable of playing the game with the skill and style needed to avoid head injuries.

"The study adds to the accumulating evidence that if you're going to play football, you should do so later," McKee said.