you can buy desktop software for 2016-2018. each year must be purchased separately and state returns are extra https://turbotax.intuit.com/personal-taxes/past-years-products/ prior to that you either have to prepare your return manually or use a pro
there is software offered on the web for years prior to 2016. that software is not up-to-date and can not be updated. so if you buy and use it, you may file a return with errors.
also if you buy the 2016-2018 from unofficial sites, you may be buying malware or software that doesn't work
