Is it still possible to e-file 2017, 2016, or earlier tax returns in TurboTax?
2017 corporate and partnership returns are the only prior-year returns that can still be e-filed. For all other prior-year returns, the e-filing "window" has passed.
This "window" lasts from January to mid-October immediately after the tax year ends. For example, 2017 personal (1040) returns could be e-filed from January through mid-October of 2018.
However, you can still prepare prior-year returns and paper-file them. Find out how.