How to determine the age of a star using asteroseismology?
Asteroseismology effectively measures the sound speed inside a star by finding the characteristic oscillation frequencies of a star.
The sound speed depends on the composition because the pressure at a given temperature depends on the average mass of a particle in a gas.
As the star gets older, it turns its hydrogen into helium, changing the composition, the average mass per particle in the gas, and hence the average sound speed.
Asteroseismology tells you the age of the star.
The answer is somewhat model-dependent, so ideally you would have an effective temperature and surface gravity in order to constrain matters. Precisions of 10% of the main sequence lifetime are possible for stars of around a solar mass. Accuracy is hard to assess since we have an accurate age for only one star - the Sun.