You must always file a tax return if your taxable income is more than your standard deduction. There is no general exemption from tax for the elderly. Taxable income includes gambling winnings, pensions, IRA withdrawals, and almost anything else. Social security is not taxable if it is your only income, but may be taxable if you have other income. You can use this IRS site to tell if you need to file.
https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return