TurboTax only retains online tax returns for the past 7 years, the same retention period as the IRS.
Tax year 2017 and earlier are no longer available.
SAVE YOUR TAX RETURNS !
EVERY year before mid-October you should save a copy of your tax return as a pdf and print a copy of it for your records. That way you will not be searching online frantically when you need it for a lender, FAFSA forms, your next tax return, etc.
https://ttlc.intuit.com/questions/1900937-why-should-i-save-a-pdf-copy-of-my-return
NOTE: TurboTax and the IRS save returns for seven years. Returns older than seven years are purged.