As much as Grey Jedi doesn't exist and Dark Side of The Force corrupts you, my version of Grey Jedi and Dark Side is different than how Most people interpreted it.
Grey Jedi doesn't just use Light and Dark Side of The Force, they are also using very Questionable methods of solving the problems and they don't just have mixture of philosophies of Sith and Jedi, but they also believe that Peaceful times makes people weak, but that doesn't mean they will fight to conquer and control Non Force Sensitive people.
They have Training of Both Sith and Jedi, which is mixture of both Meditation, Connecting to the Force, choosing apprentices or Fighting with Creatures and Their Teachers to prove their worth. They train anyway possible to get stronger and be ready for anything.
Dark Side of The Force, doesn't necessarily mean it corrupts you fully, makes you weaker or affects your aging. It is exactly the opposite. Learning Dark Side helps you to gain Balance with your Connection to The Force, but there is Chance to lose control and become Fully Invested to The Dark Side and Becoming Sith, if not being careful. The Process of Mastering The Dark Side of The Force, needs to be cautious, concentration, Strong Will and not losing yourself or Your Sanity
That's my Take and Opinion of this Matter, what do you guys think about this?