It means that you still have simpler more trusting views of people and the world in general - for instance you may have given him the impression that you think all people are basically good or trustworthy (just an example, not saying you did this). It's the opposite of being jaded or bitter from experience. Naive implies inexperience.
i think most females are naive they don't realize what's going on when it comes to relationships there naive. friends with benefits for one just a why to make girls think there not being a slut they believe that. a guy that dumps a girl for you its not love, a guy that lasts long in bed either he's not attracted to you or he has f***ed so many people his d*** ain't sensitive any more think about it a vergin cums qwick the less of a vergin you are the longer it takes or you are not attracted to that person females don't get this type of stuff so there naive.
It means he thinks you haven't turned cynical yet, because he thinks you haven't had many life experiences yet, which could be true or not. He is just making an assumption about you.
I am a bit naive too...I guess naive is someone that still see some things with a pink leans you know, like always think about the good side first, sometimes naive can be blind about somethings, like I was so naive I didn't even tought he was doing that just for me to sleep with him...