LINQ HOW TO SET DEFAULT MIN VALUE IN SMALDATETME COLUM

Came across a problem with nullable datetime columns and linq query.   Essentially I cannot query on datetime if the field is null in the database.

What is the best approach when adding a customer record with linq to sql server and setting a default value for the Date of Birth (DOB) column.

For the user the DOB is optional but I need to do a query that will return all records that have a DOB say greater than 1955.  

So what I need is a default value that is set and cannot be a valid date of birth but will also work with a linq query

For example

          var Data = from qryData in ReportData
                         where (qryData.DOB >= DOB)
                         select qryReportData;