A farmer has to purcahse agricultural land within 2 yrs of sale of Agricultural land in case the subject land was the only Agricultural land owned by him.
As per the facts your Ancestor sold the land prior to 35 years and therefore his descendants can not claim to be farmers as per the Act.
However, as a chance you can check all the form 7/12 of the village in case your grandfathers's name is reflected in any other land. If it is not then you have to follow the procedure by applying to Collector u/s 43 and 63 of Tenancy Act.
As per the recent news story Government is also contemplating to remove the embargo of farmer for Purchase of Agricultural land by charging a premium for Non-Farmers but a Policy decision is yet to be taken for the same.