Although it is only heard sung by Frank Sinatra at the beginning and end credits of Young At Heart, the title song was both a big hit for Frank Sinatra and set the tone for a very warm and wonderful Yuletide picture.

Warner Brothers already had this property, this is a remake of Four Daughters, minus a daughter, with Sinatra and Doris Day in the roles originated by John Garfield and Priscilla Lane. Doris's sisters are Dorothy Malone and Elizabeth Fraser who are all the daughters of music professor Robert Keith and all play instruments. The only non-musical member of their household is wise old maiden aunt, Ethel Barrymore.

Of course Doris sings as well. But in the passing out of vocal material, Sinatra did a lot better than she did. None of her songs did anything for her vocal career. Sinatra wisely opted for standards by some of the very best. In his role as saloon singer/piano player/music arranger Frank gets to sing Just One of Those Things by Cole Porter, Someone to Watch Over Me by the brothers Gershwin and One For My Baby by Harold Arlen and Johnny Mercer. Can't get much more talented in the song department than that group.

One For My Baby was introduced by Fred Astaire in The Sky's the Limit, but when Sinatra sang it here it became forever identified with him and a staple item at all of his live performances.

Sinatra and Day sang a duet You My Love at the finale. It was the song that Frank was working on through out the film. They sang it so well that you'd never know that tempers flared the entire time the film was made.

During the Forties when both were at Columbia Records, Frank and Doris recorded a couple of duets together. In the interim, Sinatra moved on to Capitol records so no original cast album could be made from this soundtrack. It might not have happened anyway because back in the Forties Day spoke highly of Frank. Things cooled considerably between the two of them, among the items of contention was Day's husband Martin Melcher. Suffice it to say it was not a happy set.

Still and all Young at Heart is one of the best films either of the stars did and really nice entertainment.

• While making this film, Frank Sinatra took an almost immediate dislike to Doris Day's husband, Martin Melcher, thought that Melcher was "using" her to get ahead in the movie business and tried to convince Day of that fact. When Day refused to listen to Sinatra's advice, he had Melcher banned from the set. After Melcher's death in 1968, it was discovered that he had squandered all the money Day had earned during her 20-year film career.
• This may be the only Hollywood musical that bears no music credits. Musical director Ray Heindorf had his name removed because of a new ruling that the term "musical director" was to be replaced with the credit "Music supervised and conducted by..."
• The film was untitled until Frank Sinatra's "Young at Heart" became a smash hit and was tagged onto the opening credits.