Can I file single if I have been divorced over 20 years? or do I need to file divorced? does it matter?

Divorced is not a filing status on a tax return.  If you have not remarried and have stayed single then your filing status is Single.   The software asks you some questions about being divorced to navigate you to pertinent areas in the software, but the possibilities for filing status on an income tax return are Single, Married filing jointly, married filing separately, Head of Household, or Qualifying Surviving Spouse.

Divorced is a marital status, not a filing status. When TurboTax asks for your marital status you should select Divorced (unless you have remarried). It will then ask additional questions to determine your filing status. Your filing status will be single, unless you meet the requirements to file as head of household. To file as head of household you have to have a dependent, among other requirements.