You can't create PostgreSQL database with version you want using SQL or any tool like PgAdmin.
Database version is a PostgreSQL server software version
and can be changed only by upgrading or downgrading it. This task is sometimes tricky because of some incompatibilities between versions - especially when downgrading.
It's possible to have two or more PostgreSQL running servers (the same or different version) on the same machine - they must listen on different sockets/ports.
To summarize - when you make a connection to specific PostgreSQL server, all databases you create and access are in the same version as PostgreSQL server version.