According to a Parade interview from 2007, Affleck first met Damon in the early 1980s when they were 8 and 10, respectively. The two lived two blocks away from each other in Cambridge, Massachusetts, loved baseball and acting, and went on to attend Cambridge Rindge and Latin high school.
"... Before Matt, I was by myself. Acting was a solo activity where I'd just go off and do something, act in a little TV show or something, and no one understood it. None of the other kids knew what it was I did, how it worked, or anything," Affleck told Parade. "All of a sudden, I had this friend, Matt, and he gets it and wants to do it and thinks it's interesting and wants to talk about it. Soon both of us are doing it."
During an appearance on "Conan" in 2019, Damon said Affleck defending him in a fight when they were young really cemented their friendship. Damon was about to get beaten up by a bigger kid in high school, when, at the last second, Affleck fought him off.
"I remember that was like a big moment," Damon said. "He will put himself in a really bad spot for me. This is a good friend."