Question:Is it a sin if a Christian choose not to get married for his or her whole life?
Getting married has always been an option and never a requirement. The apostle Paul never married and when persecution raised its ugly head on the horizon, he urged other Christians, if they were able, to remain single through this time of distress as well.
"Now concerning the things about which you wrote to me: it is good for a man not to touch a woman. But, because of sexual immoralities, let each man have his own wife, and let each woman have her own husband. Let the husband render to his wife the affection owed her, and likewise also the wife to her husband. The wife doesn't have authority over her own body, but the husband. Likewise also the husband doesn't have authority over his own body, but the wife. Don't deprive one another, unless it is by consent for a season, that you may give yourselves to fasting and prayer, and may be together again, that Satan doesn't tempt you because of your lack of self-control. But this I say by way of concession, not of commandment. Yet I wish that all men were like me. However each man has his own gift from God, one of this kind, and another of that kind. But I say to the unmarried and to widows, it is good for them if they remain even as I am. But if they don't have self-control, let them marry. For it's better to marry than to burn" (1 Corinthians 7:1-9).
"Now concerning virgins, I have no commandment from the Lord, but I give my judgment as one who has obtained mercy from the Lord to be trustworthy. I think that it is good therefore, because of the distress that is on us, that it is good for a man to be as he is. Are you bound to a wife? Don't seek to be freed. Are you free from a wife? Don't seek a wife. But if you marry, you have not sinned. If a virgin marries, she has not sinned. Yet such will have oppression in the flesh, and I want to spare you. But I say this, brothers: the time is short, that from now on, both those who have wives may be as though they had none; and those who weep, as though they didn't weep; and those who rejoice, as though they didn't rejoice; and those who buy, as though they didn't possess; and those who use the world, as not using it to the fullest. For the mode of this world passes away. But I desire to have you to be free from cares. He who is unmarried is concerned for the things of the Lord, how he may please the Lord; but he who is married is concerned about the things of the world, how he may please his wife. There is also a difference between a wife and a virgin. The unmarried woman cares about the things of the Lord, that she may be holy both in body and in spirit. But she who is married cares about the things of the world--how she may please her husband. This I say for your own profit; not that I may ensnare you, but for that which is appropriate, and that you may attend to the Lord without distraction" (1 Corinthians 7:25-35).
So marriage is a personal choice.