I would recommend Conceptual Mathematics: A First Introduction to Categories by Lawvere. It is written by a true pioneer. And also, you will impress your frien

I would recommend Conceptual Mathematics: A First Introduction to Categories by Lawvere. It is written by a true pioneer. And also, you will impress your friends by your hipster foray into category theory. However, this book is far from being hipster. Also, I would not be surprised if a high school student would be able to follow this book over the course of a year or two. If you titled the book: Sarcastic introduction to how simple set theory is then I would actually be fooled that it were the correct title.