The snippet below does not convert through the intermediate var2 format. You could implement a JSR-223 and use Java Date and Calendar to do the same. You might run the following untested code in ITR mode to see if it does what you want.
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Calendar;
// set up date formats
DateFormat originalFormat = new SimpleDateFormat("MM-yyyy");
Date date = originalFormat.parse( "11-2014" );
// or replace above using a property
//Date date = originalFormat.parse( testExec.getStateValue( "propertyNameHere") );
Calendar cal = Calendar.getInstance();
cal.setTime( date );
cal.add( Calendar.YEAR, 5 ); //add 5 yrs to date
Date finalDate = cal.getTime(); //return the calculated date
// save newly calculated date into a property after applying desired format
DateFormat finalFormat = new SimpleDateFormat( "dd-MMM-yyyy" );
testExec.setStateValue( "fl_datePlus5", finalFormat.format( finalDate ) );
// TODO: add return depending on Assertion or JSR step