1. is fine, though I would use the word "should" in place of "need to" so as not to sound too pushy myself.
2. Is very hard to interpret. What do you mean? Do yo mean she knew she wanted to be a nurse long before she became one, or she was acting like or trying to be a nurse even though she wasn't really a nurse? One would reflect a person's long term desire to be something, the other co
1. If your son is lazy, you need to motivate/insipire him to become a more active person.
2. She had decided to become a nurse long before she did (become one). She had just started school when she first decided that she wanted to be a nurse.
1 If your son is lazy, you need to push him to be more active. [also: "If your son is lazy, you need to encourage him to be more energetic." ... many options, depending on what you are trying to say.]
2 She thought she was a nurse before she was one. She was barely in school that she thought she was a nurse.