You didn't say whether your are using TurboTax Online or the CD/Download TurboTax software.
If you are using TurboTax Online there is no way to make it print Form 1040 if you are 65 or older.
If you are using the CD/Download TurboTax software, go to forms mode and open the Federal Information Worksheet. In Part II of the worksheet, below your address, there is a line that says "Print Form 1040-SR instead of Form 1040." Click the No box on that line.
TurboTax does not do the actual printing. It only creates a PDF. The duplex printing comes from the PDF viewing program that you are using, or from the print options that you select.
