You can Try with LINQ expression
DtOutput → System.data.DataTable
DtOutput = DtreadFull.AsEnumerable.Where(Function(x) Not(String.IsNullOrWhiteSpace(x("Column Name").ToString)) AndAlso (CDate(x("Column Name").ToString)<(new DateTime(Now.Year,Now.Month-12,1)))).ToArray.copytodatatable
Regards
Gokul