Yeah, the most recent version of Postgres provided by CentOS 5 is 8.1. And Postgres is a dependency of Virtualmin, so you’ll need to have a version of Postgres installed.
If you want to change the version of Postgres you’re using, you’d want to install a Postgres RPM.
We can’t speak for any of the RPM’s outside of what comes with CentOS itself – but you could look into RPM’s at some third party repositories, such as pgrpm: