what do you think ponyboy meant when he reflected that “Darry was just too smart to be a greasers?

Darry was too smart to be a greaser because he had responsibilities, and he decided that caring for his brothers and keeping them all together was a better route than running with the gang. He was an unofficial leader of the gang, and he tries to keep his brothers on the right path. He's given up a college scholarship to care for the boys, and he gets tough with Ponyboy when he sees him hanging with the Greasers and misusing the intelligence that can open up opportunuties.