Right.
The University.
At this time of life, Ruan Ji was still a University student, right? Both Ruan Ji and Ye Nuan, the Ruan cousins, all the girls within the family were admitted in the same university at this timeline, where Ruan Ji was already in her second year due to skipping a grade by ranking first in the special test prepared by the University for top students, who likes to graduate early.
Originally, these kind of top students get a special privilegde to skip whichever grades they want, even graduating early than others. But Ruan Ji's grandparents insisted on her stay in the University and enjoy a normal school life, that's why she decided to skip one grade to keep them happy and persued her dreams to become a sports star.
Since all the other girls were not more ethan a few months younger than her, they all joined at the same time. Yet they had to adress her as their senior in public, which was embarrasing for Ruan Liyao and Ruan Fang.