I think it's imposible retype DataRow as User, you must fill each property separately or you can use some Entity Framework which you don't want or you can have two constructors in User and fill it in one row like this:
public class User
{
public int Id{get;set;}
public string FirstName{get;set;}
public string LastName{get;set;}
public string Address{get;set;}
public User()
{
}
public User(int Id, string FirstName, string LastName, string Address)
{
this.Id = Id;
this.FirstName = FirstName;
this.LastName = LastName;
this.Address = Address;
}
}
public void SomeMethod()
{
User user = new User (DataTable.Rows[2][0], DataTable.Rows[2][1], DataTable.Rows[2][2], DataTable.Rows[2][3]);
}