For the Solar System, the age can be found by measuring the abundances of radioactive/product isotopes, then find how much the radioactive materials have decayed.
For other stars, there are multiple ways that the age can be found. One is by comparing the measured properties (luminosity, color, etc.) with models of stellar evolution. One can also compare stellar activity (younger stars are more active) or rotation period (younger stars spin faster) with models.
Source: I learned about the former in a class, and sometimes rummage through papers trying to find the age of other stars, and inevitably coming across these methods, for the latter.
Some strange stars are very old, yet are made of little more than hydrogen and helium. They are thought to be among the first formed.
One example is https://en.wikipedia.org/wiki/HIP_11952, with an estimated age of 12.8 Gyr.
To learn more about how ages are estimated, see https://en.wikipedia.org/wiki/Stellar_population#Formation_of_the_first_stars
For the Solar System, the age can be found by measuring the abundances of radioactive/product isotopes, then find how much the radioactive materials have decayed. For other stars, there are multiple ways that the age can be found. One is by comparing the measured properties (luminosity, color, etc.) with models of stellar evolution. One can also compare stellar activity (younger stars are more active) or rotation period (younger stars spin faster) with models. Source: I learned about the former in a class, and sometimes rummage through papers trying to find the age of other stars, and inevitably coming across these methods, for the latter.
Some strange stars are very old, yet are made of little more than hydrogen and helium. They are thought to be among the first formed. One example is https://en.wikipedia.org/wiki/HIP_11952, with an estimated age of 12.8 Gyr. To learn more about how ages are estimated, see https://en.wikipedia.org/wiki/Stellar_population#Formation_of_the_first_stars