It is possible to grow young.
Human body is not just a physical body; it is also at the level of mind, intellect, ego and soul. While only the physical body grows old, the other parts of human body mature with age. One also acquires more humility with age. The end result is growing young and not growing old.
One should look at biological and intellect age and not the physical age. Chronologically, you may be 70 but biologically, you may be at 60. In medical science today, most of the drugs are given keeping biological age into consideration and not the chronological age.
Most of our Vedic rituals teach us how to live young. The new epidemic of today’s era like iron deficiency, calcium and vitamin D deficiency related to osteoporosis and refined carbohydrate related heart diseases could not have entered into the society if the traditional rituals of eating gur-chana once a week, worshipping sun in the Magh month and/or not eating carbohydrates once a week was observed by the society. These were rituals meant to prevent such diseases.
Relaxation, pranayam and meditation also take one from growing old to growing young. Staying in parasympathetic mode most of the times in the day can make the difference.