“So, how long have you been dating?” the supermarket cashier asked as I swiped my credit card, my engagement ring clearly visible on the ring finger of my left hand.

It wasn’t the first time I had been asked this question. Seeing an engagement ring on someone my age — I’m 23 and graduating from Princeton in June — shocks many people. Some think I must be slightly weird, perhaps part of some strange religious sect — or pregnant.

It’s bewildering that wearing an engagement ring has opened my life to public comment.

At times my status seems to provoke anxiety about the other person’s own romantic prospects. (“I’m not even dating anyone right now!”)

Others are more direct. “You look 12,” a jeweler told me when I asked him to clean my ring. Now when people ask me how long my fiancé and I have dated, all I hear is: “How much should I be judging you for your life decisions?”

When I go home to the Orthodox Jewish community in suburban Philadelphia where I was raised, I also am judged about my relationship, but in a different way. In my community, more than half of my high school graduating class has already married, and many have children. “It’s so nice he finally committed,” a close family friend consoled me.

At home, I promise my family friends: “We are getting married right after graduation.” At college, sometimes it’s just easier to play along. “We were friends before we started dating.”

Elizabeth Yuko, a bioethicist and writer specializing in reproductive and sexual health ethics, said she is not surprised at the reactions to my engagement ring. Women, she said, often have to defend their choices and are treated as if they haven’t given careful consideration to their life decisions. “It’s part of not trusting women,” she said. “As soon as you step out of the norm,” people “feel the need to comment. The onus is on women to show that they know what they are doing,” she said.

The decision about when and whether a woman will marry has long elicited strong opinions. The 1986 Newsweek article, “Too Late for Prince Charming?” warned that a single 40-year-old woman was more likely to be killed by a terrorist than to marry. The claim was later debunked, and in 2006, Newsweek retracted the article. But the damage was done. “The article seems to have lodged itself permanently in the national psyche,” the television news correspondent Jessica Yellin wrote in a 2006 opinion piece for The New York Times.

Historically in the United States, women have married young. Even in 1970, a seminal year in the American feminist movement, the average age of a first-time bride was under 21, and the vast majority of women were married by their late 20s. But, today, the average age of first marriage is 27 for women and 29 for men, and young women today are half as likely to be married as in 1940.

Stephanie Coontz, a professor at The Evergreen State College in Olympia, Wash., and director of research and public education for the Council on Contemporary Families, suggests that perhaps the issue of marriage is so charged because it is only recently that women have had choices about if and when to marry, education and work. “For thousands of years marriage was about men making the important decisions and women accommodating to these decisions,” she said. “It is only in the past 40 years that we have said, ‘No, there is not a preset hierarchy.’”

Confused by these changing norms, people “react more defensively to people who are making different decisions” in an effort to resolve ambivalence, says Dr. Coontz.

In a stage of life where you are expected, even encouraged, to be focused on yourself and your own accomplishments, my university friends and colleagues overwhelmingly act as if by choosing to marry I have surrendered my ambitions for a different cause. It’s as if, as a young woman, I am required to pick between a profession and a marriage.

I met my fiancé when we both were doing a gap year in Israel after high school. I remember him, but he doesn’t remember me. But we both attended the same college, and had a class together freshman year. During exam week, we exchanged some supportive emails. In our sophomore year, we were both involved in an internship program that instructed us to meet with the other interns. We met up at a fountain on campus and ended up talking for hours. And then we went out the next night and talked for hours again. Away for fall break, he wrote me long emails every day. After that, he sent me a card every week. (I still have all of them in a box.)

Two years later we met at the fountain again, where he gave me a card to congratulate me on the results of my medical school entrance exam. The card contained inside references to our relationship — penguins and “Downton Abbey” — that only the two of us would know. “This is a such a perfect card,” I told him. “You should have saved it for when you propose.” He said, “I am about to.” And then he did.

My desire to marry him hasn’t changed my other goals in life. This spring I’m graduating, then heading to the University of Cambridge for a nine-month fellowship and returning to attend medical school in New York. I also am getting married to someone I love because we are certain we belong together and want to experience all of the next steps in our lives together.

Since announcing in October my plan to marry, I have gotten fairly used to the intrusive questions and the raised eyebrows. I have come to realize that people who react to my engagement may just be trying to rationalize their own decisions or make sense of mine.

Dr. Yuko told me that it would be the same if I chose to marry at an older age or to not to marry at all. She told the story of how, after college, she decided to go to Ireland for her graduate education. An older woman from her hometown tsk-tsked her decision.

“Well, you are putting yourself out of the market for a few years,” the woman warned. “But maybe you will find a professor.”