After you try to communicate with Zelda herself and sneak past many guards, you will be leaving Hyrule. When you are doing so, you will be on Hyrule field when you hear a horse noise. You will turn...
Link is in fact 10, an adult back then was 13 years or older. We cannot compare to modern guide as an adult reference so Older Link,17. Is an acceptable age and well qualified as an adult.