9% married men in their 40's report not having sex in the last year. 16% of them report having sex a few times a year to monthly. 51% of them report having sex about once a week. 20% of them say 2-3 times a week. 4% of them say more than 4 times a week.
This is based on a study by the Kinsey Institute. To find the actual table and a link to the study, search the Internet for "average is kind of sad." It should turn up at the top.
I've also seen some studies that define (something like) 6-8 times a year or less to be a "sexless marriage."
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final