When Frank Sinatra sang, "Don't you know that it's worth/Every treasure on earth to be young at heart?" he was declaring how beneficial it is to be able to ignore your chronological age and feel younger than you are.

German researchers agree. A study in the journal Psychology and Aging looked at more than 5,000 people ages 40 and older and found that those who felt younger than their years had better cognitive functioning, less inflammation and joint pain, and even lived longer than their older-feeling peers.

We’ve been telling people how to live younger longer for years. (No highly-processed foods, red meats or added sugars; lots of vegetables, fruits, physical activity, and restorative sleep.)

This German study confirms that once you've got the sassy attitude that comes with rolling back your chronologic clock, your newfound youthfulness creates a stress buffer, protecting you from stress-related conditions.

Don't look in the mirror; look in your heart. And find the joy that comes from taking good care of yourself.

Start walking (working toward 10,000 steps daily), get your diet in shape with five to nine servings a day of fresh fruit and vegetables, do strength training regularly, volunteer to help others, sleep soundly, and laugh often.

No matter how old you are today, you can feel younger tomorrow. Sixty really is the new 40. Soon, thanks to research on aging, 90 may be the new 40, and you actually may be able to reverse aging.

Dr. Mike is writing about this in his upcoming book, "The Great Age Reboot."