Unlike those relatives who can be squeezed for money, Zheng Wei and Zheng Wu are both distinguished young gentlemen. After all, the appearance of the rich in their youth cannot possibly be bad—the Jing Family has a century-long history, and solely through natural genetic selection (only marrying beauties) they can cultivate high-quality descendants.
Those chubby people were not much different in their youth either, and they would practice Combat Techniques to prolong their lives. It's just that as they age, their metabolism slows down, while the money and power they wield only increase, making it impossible for them to maintain their physique. They indulge in pleasures and become fat boys.