After 18 we can make decisions for ourselves. And we are invulnerable. We may be headed off to school. We may need someone to take care of business for us while we are at school, or during a semester abroad. So before we leave, we should have a Power of Attorney to let mom or dad handle things while we are away. Our invulnerability notwithstanding, we might have a serious illness and need someone to make medical decisions for us. And some of us may suffer an untimely death, so we should have a Will in place.