At first and until a year or two ago, this really bugged me.
By saying "not yet" it implies that one day I will be married. If I was trusting in God's sovereignty and providence, who was I to claim that I would one day be married? It felt it quite presumptuous of me to say "not yet."
That was until God taught me about hope. Hope is not wishful thinking and longing. Hope is placing my trust in a all-kind, all-knowing, all-powerful God. Knowing that he has already provided for me what I need most--Himself, a Savior, the Messiah.
I was speaking with an older single woman recently and I confided in her how my heart was changing because of hope. That it was ok for me to say "I am not married yet. I want to be. I am preparing to be a wife; when I make decisions now, I do so thinking about how it might possible impact my future husband. However, if I never marry that is ok too."
She immediately jumped on my thoughts and told me I was not at peace with being single--how could I be at peace with being single but still long to be a wife at the same time? She told me I should pray for God to either give me a husband right away or for him to completely remove all feelings of longing to be a wife. That if I was longing and He was not providing, I was not right with God.
We, as single women, hear this kind of "wisdom" all the time. I used to believe it. Now I don't.
It is possible to be both content and hopeful at the same time.
I don't know why or how God chooses to bless the way he does. But, that doesn't mean I still can't hope. It doesn't mean I can't prepare for something that might never come. It does not mean that my single years are mine to do with as I please.
Douglas Wilson explains this SO much better than I could:
[T]he time a person spends when he is single should be time spent in preparation for marriage. This is important even if he never gets married. This is because biblical preparation for marriage is nothing more than learning to follow Jesus Christ and to love one’s neighbor. In other words, preparation for Christian marriage is basically the same as preparation for Christian living. Christians are to prepare for marriage by learning self-denial, subduing their pride, and putting their neighbor first. (as quoted by Carolyn McCulley)
Oh, and by the way, now I don't mind answering the question, "are you married?" with "not yet." In fact, that is how I answer the question in English now too!