New studies on peer pressure suggest that teens, who often seem to follow each other like lemmings, may do so because their brains derive more pleasure from social acceptance than adult brains, and not because teens are less capable of making rational decisions. Peer influence during adolescence is normal and tends to peak around age 15, then decline. Teens get better at setting boundaries with peers by age 18 according to Laurence Steinberg, a psychology professor at Temple University.