This is a beautiful story. The chauffer’s daughter (Audrey Hepburn) has been in love with the younger brother David (William Holden) of the rich employer's family since she was a child. However he is a player. So she goes to Paris to get away from the drama, and comes home a beautiful blossomed woman. However the brother is now engaged, and this is a marriage to convenience to forge a partnership between two families and two companies. However, as he is a player, he spies Sabrina for the first time, and wants to leave the arranged marriage behind and go with her. Older brother, Linus (Humphrey Bogart) manages to take his place for a few days, while younger brother recuperates from an injury. His initial goal is to send her back to Paris. Slowing the affections change their loyalty. But the older brother has always been the brother who has been responsible, and would never do anything to upset the family.
As I said a beautiful story, and Audrey Hepburn and Humphrey Bogurt carry their parts well. The difference in age is something they have to overcome as part of the story, and so does not get in the way of the story.