TurboTax online is only for 2017 now.
2016 and earlier can not be e-filed or completed online. The CD/download version must be used and the return printed and mailed.
If you already paid for the 2016 version and did not complete then contact Customer Service to obtain the 2016 download. https://support.turbotax.intuit.com/contact/
If you have not paid, then you will need to purchase the prior years program.
https://ttlc.intuit.com/replies/4186197
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**