What is the difference between young and old galaxy?

Young galaxies are characterized by active star formation, often exhibiting bright blue colors due to the presence of hot, newly formed stars. They typically have a more irregular shape and contain abundant gas and dust. In contrast, old galaxies have undergone significant star formation in the past, resulting in a more reddish appearance from older stars, and tend to be more stable and elliptical in shape with less gas and dust available for new star formation. This difference reflects their evolutionary stages and the processes that have shaped them over time.