Been young at heart - Idioms by The Free Dictionary
be young at heart (redirected from been young at heart)
be young at heart
To behave in a way 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!
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.