Are you working with a HDD or an SSD? If the former, then you should not use APFS. How are reinstalling OS X? You stated it was an "old" computer. How old is it? Could you provide the exact model? It's usually in the form of a time of year followed by the year, e.g., Late-2011 or Mid-2010. To find the complete model information select About This Mac from the Apple menu. You will find it listed in the computer information.
What version of OS X are you trying to install? Do you have original Software Restore disks that came with the computer? If your computer came with Lion or later installed, then you need to use Internet Recovery to install the original version of OS X that came from the factory.