I understand you are unable to upgrade your OS X. Because for Tax year 2016: Mac OS X v10.9 or higher (64-bit is required), you would need to upgrade to that for any of the 2016 C/D/Download Version's. However, you can use a Turbo Tax Online version. I have included articles below to assist you in transferring last years tax information into an online version.
Because you are a TurboTax Premier Customer, I have included the Contact Us link at the bottom so that you do not have to pay twice.
How do I back up my tax file in the TurboTax CD/Download software?
Find Your Tax Data File in Mac
Can I transfer my 2015 TurboTax return from my computer to TurboTax Online