Yes, you can, though TurboTax FreeFile is not an option for prior year taxes.  See

https://turbotax.intuit.com/personal-taxes/past-years-products/

for the pricing of 2018 TurboTax software.

That said, there may be lower cost options for preparing your 2018 tax return.  A quick Google search brings up https://www.freetaxusa.com/file_2018_income_tax_return.jsp  as one example.  Another possibility is the free tax self-preparation assistance being offered remotely through the AARP TaxAide program which can be accessed at https://www.aarp.org/money/taxes/aarp_taxaide/ .   And, of course, you can always prepare your own form 1040 by filling in and printing the form https://www.irs.gov/pub/irs-prior/f1040--2018.pdf using the instructions https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf.  (Any related forms can also be retrieved through https://www.irs.gov/forms-pubs/prior-year ) 

Be aware that any refund due you if you file paper forms will not be processed for several months as most IRS processing centers are basically closed until the pandemic abates.  Be assured, the refund will not expire while you wait!

You can only buy the download for prior years. You have to buy a separate program for each year. They only sell the last 3 years. You need a full Windows or Mac computer to install it on. You can buy any version. All the Desktop programs have the same forms. You just get more help and guidance in the higher versions. Buy the download here
https://turbotax.intuit.com/personal-taxes/past-years-products

If you want to file for free you can fill out the forms by hand.

Here is the IRS 2018 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2018.pdf

And 2018 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-prior/i1040tt--2018.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
Sch 4 : https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
Sch 5 : https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf
Sch 6 : https://www.irs.gov/pub/irs-prior/f1040s6--2018.pdf

Prior year returns can only be printed and mailed. 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 received the return. And don't forget state.

Important! Mail Federal and State in separate envelopes and mail each year in separate envelopes.