One to two times a week is average for 30+ according to most studies (89 times per year is what I believe Kinsey found). It largely depends on the couple, and the importance they put on their sex life.
Too many factors to consider. What's your libido like? Do you work long hours? Do you have relationship difficulties unrelated to sex? Do you have children? How long have you been together? Do you live together? How's your health? Averages can mean nothing if you have a screaming baby, you live apart, you work long hours, you're under stress or you're ill. All the factors I've mentioned can have an effect on what could be considered "normal" for your sex life. Without knowing the ins and outs of your lives it's impossible to say if there's a problem or not.
