As Zoltan Zorgo provided the piece of code, it will resolve your error, but you want to get this value from db then do this
1. delete the @MA_DOB as input.
2. declare @MA_DOB as a normal variable
Declare @MA_DOB varchar(20)
select @MA_DOB = <column_name> from <table_name> where <search>
write these before your operation and do whatever you want with the value of @MA_DOB