アメリカ出身の男の子がアメリカについて紹介してくれましたって英語でなんて言うの？

Example sentences: I got to learn more about the US from an American man I know. An American lady (boy) who I have known for a long time, shared information about his country with me. A boy from the US who is familiar to me, spoke about his country at length to me. (at length = in detail)

It's always very pleasant if someone takes the time to explain to a foreign visitor some specific points or talk about items of interest within their country which may be useful or of interest to you. If you are explaining this situation later, you may say: "A young lad from the states told me some key facts about America," or, "The person who shared information about American with me was an American boy."

If the boy comes from America then he would be called 'an American boy' if he gave you details by speaking then you would say he 'told you'

"A young boy told me about America." This explains that it was a male child that first told you about America. "A young American boy introduced me to information about America." This is another way of explaining that it was a young boy that first told you about America.

When someone asks you who told you about america, two responses you can use are: "A young man told me about America. " and/or "A young boy told me about America." Both imply the same meaning that someone told you about America. You can also say, an American told me about America. Most times native speakers won't care about the gender of an informant (someone that gave you information), unless they were asking who told you, as they may know the person.