Being retired does not affect whether you have to file a tax return. The filing requirements depend on how much income you had, what kinds of income, your filing status, your age, whether or not you can be claimed as a dependent by someone else, and other considerations. There is a tool on the IRS web site that you can use to determine whether or not you have to file a federal tax return. Go to the following link and click "Begin."
https://www.irs.gov/uac/do-i-need-to-file-a-tax-return
You can also read all the details of the filing requirements in the section "Who Must File" in IRS Publication 501. You can read it online at the first link below, or download a PDF of Publication 501 from the second link.
Who Must File - read online:
https://www.irs.gov/publications/p501/ar02.html#en_US_2016_publink1000220687
Publication 501 - download PDF: https://www.irs.gov/pub/irs-pdf/p501.pdf
