confused.

okay so I've been single for five years and I started dating someone a little over a month ago... everything is going good but were not having sex like I'd like to. I try and play around put him in the mood to have sex and he tells me no.. i ask why he doesnt answer... this is the first older man I've dated too. hes in his late 30s. is this something to be considered about or am I over thinking the sex part of being with someone.