Too big of an age difference?

So last summer I met this guy at a concert, he was super cool and we have a lot of things in common! We talked for a long while and then after that he got my Snapchat, but that was that. We didn't really Talk much, I mean we did a few times but that's about it. Just two weeks ago I was at another concert and he came up to me. He obviously saw me which I was surprised he remembered me. Anyway we've been talking more now, and he really wants to hangout, and so do I! The only problem is that I'm 17 and he's 20. My best friend says I shouldn't hangout with him because he's 20, but I know my limits and how to say no to things I don't want to do. I need someone else's option😫