Secondary aging: age-related changes that are due to social and environmental influences, poor health habits, or disease. Prosperous nations with high levels of social inequality experience poorer overall health (us, uk) than less wealthy but more egalitarian societies (japan: canada has distributed it"s social and economic resources fairly equally among citizens and therefore. Canadians have experienced relatively good health: however, income inequality in canada has been increasing since 1980"s, adversely impacting overall health. Image: remaining hale (years) at age 25, by income and sex, in canada from 1991-2001: the brain & nervous system. In late teens, developmental processes reach a balance and brain attains stable size/weight: by early adulthood, most functions have become localized to specific areas of the brain. This may depend on the ability of the frontal lobes of the brain to regulate the limbic system: limbic system: the part of the brain that regulates emotional responses (think before you do/say something, emerges in early adulthood.