A consistent culture expects group adherence at all ages, in all settings. We are the best example of an inconsistent culture. A country like Japan is a consistent one, and western Europe is somewhere in between. My husband has ADHD and has taken Ritalin and Zoloft for about 6 years with BIG improvement. There's no doubt in my mind that aspects of behavior we ascribe to personality is genetic.
Studies show qualities of impulsivity are transmitted from one generation to the next.
What's different is where each community and each society draws its line between abnormality and normal variations of temperament. Finally, one's genes are only a tendency or proclivity toward a behavior. They are not mandates or blueprints. Except in extreme situations, environment can make a difference. Once again this is neither nature or nurture, it's both.