You're so young, and I'm thinking you don't know what marriage means.
5 seconds sound clip from the Gone with the Wind (1939) movie soundboard.
You can hear this line at 00:30:11 in the Blu-ray version of the movie.
Quote context
[...]
- Don't you? Don't you want to marry me?
- But you can't! Not if you care for me!
- Oh, my dear, why must you make me say things that will hurt you?
- How can I make you understand?
- You're so young, and I'm thinking you don't know what marriage means.
- I know I love you, and I want to be your wife.
- She's like me. She's part of my blood and we understand each other.
- How could I help loving you? You have all the passion for life that I lack.
[...]