You can still file your 2016 tax return but TurboTax Online is only available for the current tax year. Also, you won't be able to e-file the return you will have to mail in a paper return. If you owe taxes, you will be subject to penalties and interest for late filing and late payment. If you are getting a refund, there is no penalty.
See How do I prepare a prior-year tax return? for more information:
https://ttlc.intuit.com/replies/3301770
