Final answer:
The rotation speed of the Galaxy is not directly used to date the age of the universe, unlike the Hubble Law, white dwarf stars, and star clusters, which are all methods used to estimate its age.
Step-by-step explanation:
Among the options provided, the rotation speed of the Galaxy is not a means to date the age of the universe. Methods such as the Hubble Law are used to estimate the age of the universe by relating the recessional velocity of galaxies with their distance, which implies an expanding universe since the Big Bang. Similarly, white dwarf stars provide another method known as white dwarf cooling, where the cooling rates of these stars can be used to infer minimum ages for different components of the universe. Radioactivity dating, such as those using radioactive isotopes, is employed more in geology and archaeology than in cosmology. Finally, studying star clusters helps in assessing the age of the universe by calculating the age of the oldest star clusters, which gives a minimum age of the universe. However, the rotation speed of the Galaxy does not directly inform us about the age of the universe, but rather it can give insights into the mass distribution within the galaxy, which is of separate interest.