Get your taxes done using TurboTax

In TT 2017, if you were running 10.11 or less, you got a warning screen.  
You appear to be running 10.11 now, so you will at least need to upgrade to 10.12.  There is a manual way to do this if the App Store installer wants to bump you to 10.13 or higher and you don't want to do this.