He does seem to like you a lot which is the good thing. As for the bad thing, why do you think it is that he went from wanting more on that initial passion to saying it's the "maximum" that he could give you? Have you discussed why? Is he wanting to wait and for what/how long? Is he having problems with his drive that he'd benefit from a doctor? Is something else going on?
So my first suggestion is just to try talking things out. My second suggestion is to act. So what if you're younger? Keep kissing him. Start to undo his pants. You may not have the experience to do everything but I'm sure you would naturally at least know how to do some stuff, just go for it
Hopefully he responds and if not, then you guys will have some things to talk through and figure out.