The earliest possible date for Western easter is March 22nd.
So, by Western reckoning, Easter can be on March 25th, but not by Greek Orthodox Church practice. This is because the Greek Orthodox dates are based on the Julian calendar, which calculates Spring Equinox differently.
There are a few Orthodox sects which operate on a still different calendar. These "Old Calendarists" follow another version of the Orthodox Calendar. I have not been able to determine if calendar this allows for an earlier Easter.
This resource by Marco Montes provides a calculator for three types of Ecclesiastical calendars, which may be useful.
From a travel perspective, Eastertime weather is usually very pleasant and there are always special Easter trips to Greece. The Greeks sometimes go away for Easter as well, if they are not returning to their home island or celebrating with friends and family, so there are often good package deals available for Eastertime travel throughout Greece.
More About Greek Easter:
Pictures of Easter in Greece
Easter Vacations in Greece
Preparing the Greek Easter Lamb
Greek Easter Greetings
Read Even More About Greek Easter