In fact, preschool-age children who are overweight before age 5 are five times more likely to be overweight at age 12 than those who were not overweight before age 5, a new study finds.Another data suggest that levels of physical activity decline precipitously in girls in the United States during adolescence. Although the decline in our study began at the outset of adolescence, its rate accelerated so that by the ages of 18 and 19 years, the majority of the girls engaged in virtually no habitual physical activities other than those performed during school.