My older brother was my hero when I was growing up. This is the correct option. The writer is setting the focus on one fact. He/ She thinks this fact is emotionally important and this emotional view is reflected through the words" my hero". Besides, the speaker is talking about his / her brother.
These options are not right:
-When I was young I was the smallest one in my class. This may belong to an autophiography because the writer refers to a specific time in his/ her life: "When I was..." and the information he / she gives is objective.
-Daniel hit the ball so hard it flew out of the park. This refers to a third person and the link between this person and the writer is not given.
-Natalie’s family went to the seashore every year. The same as avobe.