TurboTax Online in for the current year only (2019). However, you can use the desktop software to file previous years' tax returns. Please note that these returns (2018 and before) can not be electronically filed and will require mailing. The IRS will process mailed returns when it resumes full operations, hopefully very soon.
If you are asking whether you can still e-file your 2018 return I believe the answer is no. The e-filing window for a given tax year runs from Jan-Oct of the following year. You can file a paper return for previous years. https://ttlc.intuit.com/community/e-file/help/is-it-still-possible-to-e-file-or-earlier-tax-returns-in-turbotax/00/25946
Online preparation and e-filing for 2018 is permanently closed.
To file a return for a prior tax year
If you need to prepare a return for 2016, 2017, or 2018 you can purchase and download desktop software to do it, then print, sign, and mail the return(s)
https://turbotax.intuit.com/personal-taxes/past-years-products/
Remember to prepare your state return as well—if you live in a state that has a state income tax.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Note: The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac. It cannot be used on a mobile device.
If you are getting a refund, there is not a penalty for filing past the deadline. If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return