"He is a man and I am a boy."
번역:그는 남자고 나는 소년입니다.
There is a difference between 고(이고] and 과(와) even though that looks same in English. Two words are used like "AND" in english. But when you say "~고", that connects two different sentences, and when you say "~와" -actually after the word like 남자, 와 is proper than 과- it is to link two different names.