This varies from person to person. There is a point in time at which hormones in a persons body begin to loose their effective functions, a period I have heard reffered to as adult puberty. In women this is marked by menopause. While you can still theoretically maintain a healthy body at this time, it becomes increasingly difficult. Maintaining a healthy diet and constant exercise are essential to achieving this. A doctor won't tell you much more than this.
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Being healthy is a positive trait. But i don't think it is realistic at a young age. But if it's a high school maybe.
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