You have now seen H-R diagrams for many different star systems. H-R diagrams can tell you about the ages of star clusters. For instance, a cluster with a lot of blue giants is very young, because those stars burn out very quickly. A typical middle age cluster has most of its stars on the main sequence. An older cluster has a lot of red giants. As the cluster ages even further, you see an increasing number of white dwarf stars.
Research Challenge. Find a cluster of stars that intrigues you. You may find a few others on SkyServer, but you should look at other data sources as well. Good places to look include the Hipparcos database, The Palomar Observatory Sky Survey, the Mulitmission Archive at Space Telescope, SIMBAD, or another data source you find online.
Create an H-R Diagram for your star cluster. Deduce as much as you can about the age and distance of the cluster by studying its stars.