Ages of stars when they fall below threshold values for their X-ray luminosity (left panel) and X-ray flux in the habitable zone (right panel) as functions of stellar mass. In both panels, each colour represents a specific choice for the threshold value and the lines from bottom to top for each colour shows the values for slow, medium, and fast rotator cases. In both panels, the y-axes are logarithmic for ages up to 1000 Myr and linear at later ages.