It means that whatever "they" are makes them feel young again.
In the Heart of the Young was created in 1989.
For the Young at Heart was created in 1960.
Because your old and you want to be young again.
Young Heart was created in 2005.
The duration of The Young in Heart is 1.5 hours.
The Young in Heart was created on 1938-11-03.
Advice for the Young at Heart was created in 1987.
Yes you can but sometimes it's not a good idea to get your heart broken at such a young age.
The Story of a Young Heart was created in 1984-08.
No, 35 is not too young to have a heart attack.
Songs for the Young at Heart was created on 2007-02-26.