While I will agree that there are some who choose to wait until marraige, and do so successfully, that is not the norm. As for those who now wish they had waited, the fact still remains that they didn't wait. Most people will not wait until they are married to have sex, and that has been consistent over time. Even during the period when our values were much more conservative regarding premarital sex, it was occuring on a widespread basis (studies done in the 1930's, 40's and 50's). Just because it wasn't talked about, or wasn't admitted to doesn't mean that it wasn't occurring.
With individuals marrying later in life, to expect that people will wait until marraige to engage in a sexual relationship is, in my opinion, unrealistic. Chances are much greater that people will not wait until marraige that they are that people will wait.
So, no, the women you have spoken to have a feeling that is not unrealistic. But that feeling also occurs after they have already engaged in premarital sex. Hindsight is 20-20. I'm certain there are any number of teenagers who also say, once they have experienced the consequence of being pregnant at a young age and not married, say they wish they had waited. But the fact is, they didn't. Feeling regret after the fact does not appear to prevent premarital sex. And telling teenagers that they will be sorry later is ineffective because no matter how many negative consequences they are warned of, teenagers, by nature of their developmental stage will always believe, "That was you. It won't happen to me."