Yes, you can restrict entries only from the admin user. In the following code, Added_User stores the name of the user who added the current record and zoho.adminuser returns the name of the admin user. If the added user name is not equal to the admin user name, the record will not be added. The code is added on add -> validate block of the Script tab.

            if (input.Added_User  !=  zoho.adminuser)
            {
                alert "You are not authorized to add records";
                cancel submit;
            }

Note:

Zoho Creator automatically tracks details about when and by whom a record was added or modified using the fields Added User, Added Time, Modified User and Modified Time. This information will be displayed in the view, if the columns are selected from Column Properties option of the View tab in Edit mode.  Refer the topic, Display User name and time, for more information.