It’s a difficult question to answer but generally speaking, there is no such thing as a person who “shouldn’t reproduce”. Primarily because it is hard to delineate where this alleged line is, and it easily turns into a case of eugenics where any slight problem supposedly means that a person shouldn’t reproduce. Moreover, it devalues life in saying that possible complications means that life isn’t worth being brought into this world. A culture that deems hardships as making life not worth living is a defeatist culture, not a Christian culture. A defeatist culture is constantly looking for excuses to deem life too risky, or too inconvenient, or too hard, but the only thing in the world that makes it better to not have been born is the rejection of grace, and that is because the spiritual life of the person is executed and the universal vocation (to love) is lost forever.
It’s always true that a person might be better prepared for children after X point, but this is also fallacious because nobody is ever really ready for children, or for religious life, or for priesthood, and that is because we are in a state of being sanctified until the day we die, or at least we ought to be. “Being sanctified” means “to be made holy”. “To be made holy” means, “to become a better version of yourself”. So, the cases where it would be better not to have children are grave cases of sin, not venial sin. For example, if you have no intention of raising & taking care of the child, then it is good not to have a child. But, if sinful means are used to not have that child, then it is still wrong to do those actions, though perhaps not as wrong as otherwise completely ignoring future consequences.
That being said:
A marriage is good from the instant the sacrament is given, even without children, and even if the marriage never produces children. “Be fruitful and multiply” is the first command in the Bible and it is a foreshadowing of the superlative version of this command, which is to spread the Gospel to others. “Gospel” means “Good News”. The Gospel, when it is heard and brought into practice, brings a person into the Beatific Vision; to eternal life with God. To desire and bring eternal life to another person is to will the highest good for them. “To will the good of another” is to love, and “to will the highest good of another” is to love perfectly. People of all vocations, including [and often especially] those who do not bring children into the world are able to fulfill the command “be fruitful and multiply”.