There's no definitive age for the globular clusters, but they are believed to consist of population II stars and therefore very old.
As a ball park figure, they are probably around the 10 billion years old mark.
In our Milky Way galaxy, globular clusters tend to be at the "outlying fringes" or "halo" of the galaxy, and seem to be largely made up of very old stars.
"The halo primarily contains individual old stars and clusters of old stars ("globular clusters"). It may be over 130,000 light years across. The halo also contains "dark matter," which is material that we cannot see but whose gravitational force can be measured." to shorten the answer - individual stars, clusters, and dark matter.
The center of the Local Group is home to the Milky Way galaxy, which contains a collection of ancient stars known as globular clusters. One of the most notable globular clusters is M13, located in the constellation Hercules. These clusters are densely packed with old stars and provide insights into the formation and evolution of galaxies.
Rigel and Deneb are not part of aging globular clusters. Globular clusters are tightly bound groups of old stars that orbit around galaxies, while Rigel and Deneb are individual bright stars that are not associated with globular clusters.
The hottest stars. Generally, globular clusters contain mainly old stars, population II stars
10-12 billion years old.
a globular cluster
The cluster that contains a group of older stars located in the halo of the Milky Way is known as a globular cluster. These clusters are tightly bound together by gravity and typically contain stars that are very old, often several billion years. An example of a well-known globular cluster is M13, also known as the Hercules Cluster, which is situated in the constellation Hercules. Globular clusters are important for studying the early history of the galaxy and the formation of stars.
Open clusters are loosely bound groups of young stars that are found in the disk of a galaxy, while globular clusters are tightly packed groups of old stars that are found in the halo of a galaxy. Open clusters have fewer stars and are more spread out, while globular clusters have many more stars and are more densely packed. In terms of composition, open clusters contain mostly young, hot stars with higher metal content, while globular clusters contain mostly old, cool stars with lower metal content.
A globular cluster (without "galaxy") is a large group of stars, in form of a sphere, within a galaxy. A galaxy may have thousands of such clusters. I am not sure whether the term "globular cluster galaxy" has any meaning in astronomy. It might be a galaxy with a lot of such clusters.
Astronomers believe the globular clusters are made of old stars because of the lack of heavy elements. The heavy element is very abundant in stars like our sun, so the theory is the globular cluster must be older and formed in a more primitive universe.
Actually the terms "Globular" and "Open" are not related to the number but the age of the stars. Globlular clusters are many old stars packed in spherical form (they look like hazy mothballs to the naked eye) and "open clusters" are many young stars formed close to each other. The constellation Pleiades is an example of open cluster.