This depends ENTIRELY on several factors: the age of both partners and their emotional maturity levels, the type of relationship that exists, and the ability to consent! If both consenting partners are 23 or 37, and the relationship is a "casual sexual encounter", there is no problem at all! On the other hand, if both partners are 15, in a serious relationship, and it's their first sexual encounter, but one person is nervous about having it too soon... having sex too early can not only hurt the relationship, but it can emotionally hurt the person who wasn't really ready! Each situation is unique, though. Remember that NO ONE enters a relationship thinking it's doomed to fail-- dating exclusively exists as a way to determine compatibility for marriage-- but since only a small percentage of relationships become marriages, if you're only doing it because you think they're "the one," then you might want to think things over!
Look, think about it this way~ if you were to break up tomorrow, would you regret having sex today? Consider this question, and you will have your answer <3 Hope this helps!