Eleanor Parker was born on June 26, 1922 [1]. "The Sound of Music" was released in 1965. To determine her age during the film, we need to calculate the difference between the release year of the movie and her birth year.

Calculation:
Year of "The Sound of Music" release: 1965
Year of Eleanor Parker's birth: 1922

Age during "The Sound of Music":
1965 - 1922 = 43 years old

Therefore, Eleanor Parker was approximately 43 years old when she appeared in "The Sound of Music" [2].

Learn more:

1. Eleanor Parker - Wikipedia
2. Eleanor Parker dies at 91; played baroness in 'The Sound of Music' - Los Angeles Times
3. 'Sound of Music' Baroness Dead: Eleanor Parker Was 91