Can i file my 2018 and 2019 taxes now

Sorry, Online for 2019 and prior is closed now so you can not start a new 2019 or prior return or finish one. Online is only for 2020. Oct 15, was the last day to efile.  2019 is now the prior year. If you entered 2019 into the 2020 online version you should clear out your online return so you can use it for 2020.
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444

Did you start an Online return? How to finish a prior year online return
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/00/26322

Or How to file a prior year
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25984

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. Buy the download here
https://turbotax.intuit.com/personal-taxes/past-years-products/

You have to print and mail prior year returns. 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. Don’t forget state.

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

If you are getting a refund, there is not a penalty for filing past the deadline. You have 3 years to file for a refund. 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.

If you want to file for free you can fill out the forms by hand. Here are some basic forms…..

Here is the IRS 2019 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2019.pdf

or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2019.pdf

And 2019 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2019.pdf

2019 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2019.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2019.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2019.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2019.pdf

Then when you do file 2020 enter 0 for the 2019 AGI since you are filing 2019 late.

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

And 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

IRS 2018 Schedule A Itemized Deductions
https://www.irs.gov/pub/irs-prior/f1040sa--2018.pdf

IRS 2018 Schedules 1 thru 6 (only if needed)
https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf
https://www.irs.gov/pub/irs-prior/f1040s6--2018.pdf