Can't format drive to APFS on older machine prior to 10.13 install
If you create a High Sierra USB installer, then you should be able to use the Disk Utility application to format the SSD as APFS before installing macOS.

If you boot from Internet Recovery using the Option-⌘-R keys then you should get the Mojave Disk Utility application. This can also be used to APFS format the SSD. Note: You have to have had macOS Sierra 10.12.4 or later installed before being able to use the Option-⌘-R keys.