I'm sure they have good intentions, but I don't know what to make of such comments, and usually don't inquire what exactly they mean by them. That they don't think they could deal with a lifetime without physical intimacy? (It's not my idea of a good time either, but seems necessary under the circumstances.) That they are afraid of being by themselves, or facing so many aspects of life alone? (Nor am I thrilled about those prospects, though there are ways to compensate.) That they so find their identity in being a wife/mother or husband/father that they wouldn't know who they are without it? (True, that's a problem I do not have!)
Well, I'll say here what I would probably never say to someone directly, because it sounds too harsh / religious: God's grace is sufficient for me, and his power is made perfect in weakness. It's true for me, and I need to remember it. God's grace is sufficient for a lifetime of singleness. Really. Isn't that amazing? It may not come to that for me, but if it does, it's going to be OK.
It's true for my married friends, too, looking at their spouses and children, feeling helpless - wondering when someone's going to "find them out" and tell the world they aren't really grownups and should not be allowed to have these responsibilities! God's grace is sufficient for you. His power is made perfect in weakness.
"But we have this treasure in jars of clay to show that this all-surpassing power is from God and not from us." - 2 Corinthians 4:7 (click to read in context)Living as people of the gospel means that we know and experience what it means to put our lives in God's hands and say: You're God and I'm not. I put myself at your disposal, recognizing that what you'll do with and in my life is way better, ultimately, than anything I could come up with. So I'm willing to give up what I might think are my "rights" - including the "right" to be married, and even the "right" to be happy - in favor of what you want to do. Your kingdom come, your will be done, right here like it is in heaven. And if it's hard and I mess things up more often then not, that makes it all the more clear that it's not about me and some ability or virtue I have - any power here is coming from you, not from me.