Is remaining unmarried while maintaining chastity, while being Makruh, considered sinful and is a person who chooses this path subject to punishment?
It is not something that causes punishment in the hereafter, but often people are happier or more stable in life when they get married (even if it has its own challenges!).
If you are young and don't have an obvious reason not to get married, if an opportunity that feels right comes up, it's nice to at least try to explore the possibility of getting married, so you don't look back and feel like you missed out on something. But everyone has their own path in life and sometimes one path is not for everyone.