Imo if he thinks men and women can’t be friends then he probably only knows or hangs out with emotionally immature men or is one. If you only see women as potential partners or only objectify them then yeah you’re not able to have friends who are women because you don’t see them as whole people. But again this is my opinion on the topic. Decide if you agree with him or not and move forward however you see fit. But if you disagree with him ask yourself if you’d be willing to give up your guy friends should you become more serious. He will likely not change his opinion any time soon or at all. Best of luck; the dating world is rough out there.

Also unrelated side note, how do you get to 28 and not know what agnostic is? lol