Due to Time dilation, time is perceived differently at greater speed.
Time dilation is an actual difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from gravitational masses.
Time dilation explains why two working clocks will report different times after different accelerations. For example, ISS astronauts return from missions having aged slightly less than they would have been if they had remained on Earth.
And, we know the Flash can run even faster than light.
Is the effect on his aging ever mentioned anywhere?