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!
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?
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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.
Farlex Partner Idioms Dictionary © Farlex 2017