M67 is an open cluster of stars in the constellation Cancer. It is approximately 2,700 light years distant. The age of the cluster is about 4 billion years old. This is very old for an open cluster. Only a few open clusters are found to be older than M67. The age of M67 is the same order of magnitude as our solar system and many of its stars have the same chemical composition as our sun. This makes M67 an appropriate object for study of solar-type stars. More than 100 sun-like stars have been identified in M67.
1http://www.seds.org/messier/m/m067.html