Stellar evolutionary track of X-ray luminosity from Johnstone et al. (2021a, CJ+21). The age of K2-18 is adopted from Guinan & Engle (2019). The dotted lines show the evolution track generated with MORS for different percentiles of the rotation distribution: (red) fast rotator, (green) medium rotator, and (blue) slow rotator. The measured X-ray luminosity is almost an order of magnitude lower than the expectation from the model.