I'm married and still go out *sometimes.* The fact that I go to less shows now has nothing to do with me being married. My husband is always telling me I should go out more. I have a kid too. Kids are more of a drain on your social life than being married, but I don't think I've ever really felt "held back" because I have a kid.
The reason I personally don't go to shows anymore, for the most part, has to do with the fact that I live in the same fairly small town that I've lived in my entire life, and after a while I just get sick of seeing the same bullshit from the same people over and over again. I love going out if there's a band playing that I genuinely like and enjoy listening to. If it's a mediocre band that I don't care about, I'd just as soon stay home. There are plenty of people in Lafayette that use "going to shows" as an excuse to get wasted and act like idiots.
Personally, I would rather get drunk in the comfort of my own home where I have a nice bed and records I actually like to listen to.
I'm also a pretty dedicated student, as un-punk as that is, so if there's a show on a weeknight chances are I won't be able to make it. School has been WAY more of a constraint on my schedule than marriage/parenthood ever has.
I'm only 22, so who knows what I'll be like when I'm 25. Or 30.