Rules governing sale of residential property in the case of senior citizens

I am a senior citizen, aged 70 years, retired from private service long ago and presently live with my wife in Kochi under the care of my son in a rented flat. All through my career life, I was employed with small trading firms and small scale industries. As my earnings never crossed the tax exemption limits, I have never filed any tax returns. Moreover, my employers never maintained any proper records of employment for their own reasons. While I was working in Gujarat, I had booked a house with a builder there and with his help I was able to get a loan of 2 L from BOB for this purpose, which was paid back in instalments of Rs. 3400 and I had to take up many part time jobs to make the repayment possible. I was given possession of this property in 1998. The cost of the tenement at that time was 2.9 L. Except this property, I don't have any immovable or moveable property anywhere. I also do not have any income from any source except some interest I receive on 2 FDs deposited by me long ago.The present total maturity value of these are around 5 L. I have been filing form 15H for this for exemption from deduction. We depend entirely on our son for our living. Recently, I sold this property for 29.75 L and deposited the money in bank FD account. Some people known to me says that I have to buy a property for this amount within an year, failing which tax @ 20℅ will have to be paid on it. Others say there is a two years time period for it and also if I buy a plot and construct a house, I will get 3 years time for it. I would like to know what actually the rules say in this regard. Though I have carried out some extension work as well as regular maintenance work during the twenty years of my ownership, I don't have any bill for it. Moreover, finding a suitable property within an year is very difficult. Buying a suitable property is not anything to be done in a hurry. So, what should I do in such a case? Is there any provision in law for a senior citizen having no source of income to keep this money in bank and take care of his expenses with the interest he receive from it, so that he doesn't have to depend on anyone? Please reply at your earliest. Thanks. Mamachan Joseph.