This chemistry thing is very dangerous in the meaning that it puts rose-tinted glasses on and you’re unable to see things as they really are. Don’t rush into “hitting it off” in all sorts of meanings. Observe the guy, the way he behaves, if he pushes you for getting intimate or if he acts with respect towards you. Believe me, as a thirty year old I can wittness there are herds of creeps around, who have little care about your feelings – you’re just another beautiful to girl to them, so they’ll charm you, even future fake you (I think we could be a great couple, etc.etc., without actually ever delivering that to you) in order to get everything that they can from you. I’m not saying he is neccesarily that sort of guy, but you really have to watch is his actions and words match, especially having in mind he is much older than you, and therefore much more cunning in these matters. For me personally guys who chase very young girls are somewhat suspicious, cause its very very rare that people of that different age (I assume you are around 20? and he is around 40?) would have something common except the bed.