Has nothing to do with "growing up". In our overpopulated world, I'd say not having kids is the responsible thing to do! I also feel that 'coupling' has been brainwashed into us. I've always felt that way, and still feel that way, even though I have an SO.
We don't need to couple or have kids to be grown up or responsible. I like my life, I am active, I am busy, I have a job, I pay my taxes, I help out friends when I can...
I respect people with spouses (and ex-spouses) and children... but I don't think they are grown up and I'm not.