You can, but you cannot file them Online, the Online version is only for the current years return. To file your 2016 return with TurboTax you need the 2016 Desktop software & the return must be mailed, you cannot e-file a prior year return in TurboTax. You can purchase the 2016 Desktop software from TurboTax at the following website.
https://turbotax.intuit.com/personal-taxes/past-years-products/