You cannot file for free using TurboTax for tax year 2018 thru 2016. The TurboTax online edition which include the Free edition are only for tax year 2019.
To complete and file a tax return for prior tax years (2018 thru 2016) using TurboTax you would need to purchase, download and install on a personal computer, Win or Mac, one of the desktop editions for each tax year needed from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
Prior year tax returns can only be printed and mailed, they cannot be e-filed. Use separate envelopes for each tax year when mailing multiple year tax returns.
