AD Brutus Symmetry is a Photoshop Creative Cloud Panel that provides tools to work with -almost- realtime symmetry.

Brutus is Adictive! Awesome for Character design! Fantastic for Brainstorming!

As there is no default tool to create real time symmetry in Photoshop versions older than CC2018 this panel is the closer approach you could have. It basically uses Photoshop guides (vertical and horizontal) as Axis for the symmetry, but it’s not limited to guides, it also works with selections and for fastest use we can assign shorcuts to the main functions.