DAG setup

Howdy,

Running Windows 2008 R2 SP2 and Exchange 2010 SP2, both are enterprise

I am in the process of setting up a DAG and when I go to add the database to the DAG the “add mailbox database copy” option is not available for any of the older databases that I have running and want in the DAG.  When I create a new database, I get this option when I right click on it. How do I go about adding the existing databases to the DAG?

Thanks,