Without doubt - a naturopathic diet, 8 hours sleep, daily exercise (about 2 hours and 10 minutes of walking per day. No smoking. No drinking. No recreational drugs. No sugars and/or starches.
Evidece. I'm 65. I have had trouble on three continents proving I'm over 60s. I look in my mid 40s.
My sister lives a similar lifestyles, as do many friends. We all look young.
My sister at 62
Me, earlier this year, at 65.
Neither of us had any work done ever.
Neither of our parents looked this young at our ages, and both of them had serious health issues.
I would say that the biggest factor in looking young is early exposure to good living habits.