A Harvard study of people ages 18 to 45 found that the more time adults spent exercising, the more brain tissue they had in zones involved in memory. Memory-related brain areas start shrinking at a rate of 1% to 2% a year after the age of 50, according to researchers from the study. But you may be able to slow the decline with exercise. Aim for 150 active minutes a week, and don’t stop as you get older. Keep going!