be, stay, etc. young at heart

be young at heart

To behave in a way or have a disposition that is more youthful than one's age. Grandma is still so young at heart—I can't believe she's taking dance lessons at 90 years old!
See also: heart, young

stay young at heart

To maintain behavior or a disposition that is more youthful than one's age. I can't believe Grandma's taking dance lessons at 90 years old—how does she stay so young at heart?
See also: heart, stay, young
Farlex Dictionary of Idioms.

be, stay, etc. young at ˈheart

(of an old person) still feel and behave like a young person: He says that the secret of living to 100 is to remain young at heart.
See also: heart, young
Farlex Partner Idioms Dictionary
See also:
  • be young at heart
  • have (one's) heart in the right place
  • have heart in the right place
  • get intimate with (someone)
  • be intimate with (someone)
  • be set in (one's) ways
  • be set in your ways
  • carry a secret to (one's)/the grave
  • carry a secret to the grave
  • Graves