Your talathi is correct. Only farmer can purchase agri land. If any one is not farmer, then he will have to convey administration that he will do farming. So if you want that land then apply to concering tahsildar or sub divisional officer. And convey him that you will use that land only for farming. You may get that land.
And as you said you are grand father was farmer, then you should not have any problem. You can purchase that land. If talathi not co-operating, contact immidiately to tahsildar.