Jiwen and Sungeun,

Your summary is accurate and informative everywhere but in the second half or the first sentence ("but he just wanted to become a migrant farm workers twenty years ago"). If you change "wanted to" to "was," it is accurate. 

The grammar and punctuation are fine except for the last sentence of the first paragraph ("So he had to head north.") "So" cannot be the first word of a sentence. "So" is a conjunction (like "and" and "but," and connects sentences in the middle. The correct sentence is: "He became a teacher by the time he was 18, but he was unable to provide for his family, so he had to head north."

 

 Alfredo Quinones-Hinojosa  is a neurosurgeon and professor at Johns Hopkins University, but  he just wanted to become a migrant farm worker twenty years ago.He was born in Mexico,and by age 5, he was working at his father's gas station.He became a teacher by the time he was 18, but he was unable to provide for his family.So he had to head north.

       He lived in the fields in a broken-down camper he bought for $300. He signed up for English classes at a community college. He went on to Harvard Medical School.Then he received his U.S. citizenship