Need some man advise 😬?

I started talking to a guy a while back and have been finding out some rather unsavory things about his past and his family. I'm pretty sure by the way he's acting that he's starting to catch feelings for me and I'm definitely not catching them for him. He's a nice guy now and all but I don't want to be anything more than just friends. Also he's 28 and I'm only 20 so we are just in different stages of life where he's ready to move faster in relationships which is why I think he's been trying to move fast with me so I don't want to let him think there is a possibility of anything with me for very much longer. How do I subtly let him know that I'm never going to be into him that way.