I am trying to determine in what tax years I failed to file taxes with both the Federal government and the Colorado State government. To the best of my knowledge I think I have to file for all years going back to 2016.
You can check your online account with the IRS and look for transcripts of federal tax returns you have filed. You will have to contact your state to ask them how to check the state records.
https://www.irs.gov/individuals/get-transcript
https://www.irs.gov/payments/your-online-account
If you have not been filing your tax returns for many years, you should make every effort to get caught up. You may owe tax due with penalties and interest, and your future Social Security benefits may be affected if you have not been filing tax returns.
TurboTax software is only available for as far back as 2020. There may be other tax software available for longer ago--you will need to use Google to search them out. Or seek local paid tax help.
It might be better for you to seek local paid tax help in a situation when you are several years behind in filing your tax returns. Do you even have all of the documents you will need to enter and show your income—like your W-2’s and any 1099’s?
It is too late to receive a federal tax refund for any year earlier than 2021----earlier refunds have been forfeited. But if you owe tax due, you will always owe it until you have paid--including the late penalties and interest. A tax professional may be able to help you negotiate with the IRS if you owe a lot.