How to filter records from DataTable for a condition ">=" ?

Question

I have a datatable with columns like First Name, Middle Name, Last Name. I need to filter the records in C# for a condition like shown below.

Select * From Table Where LastName >= 'john'

How to apply this where condition and get the filtered results set that will have records whose last names are like John, Justine, K*****, L***, M***.....Z*** ( last names from J to Z as per alphabetical order)

 

This datatable is populated by executing a stored procedure and I can't apply the filter at stored proc level as data is encrypted in backend.

 

I'm able to get the results for equality operator using the below logic.

e.g. 

SQL vesion:  Select * From Table Where LastName like '%john%'

  

C# version: 

var employees = ( from e in dtEmployee.AsEnumerable()
                       where e.Field<string>("LastName").Contains("john")
                       select e ).ToList();

 

Similarly, need to use the >= operator. How to get records for this filter condition? Can anyone please help on this?