Mr. Belvedere Rings the Bell (1951)
Mr. Belvedere Rings the Bell is a 1951 comedy film, the third and final one starring Clifton Webb as Lynn Belvedere. Mr. Belvedere lies about his age and lives in a senior citizens home to determine if there was any point in growing old. As a result, he inspires the residents of the senior citizen home that even at an older age, life is worth living if you use your imagination.
More at Wikipedia.