Wondering if it might work better instead of addressing the video game playing head-on, to come at it sideways?
What I mean is: come up with a goal for your son. Would be ideal if he could set that goal, but if not, set a small attainable goal for him. Something like: Get groomed properly each day. Make his video gaming dependent on the grooming happening first.
Then after that has gone well for awhile, add another attainable goal. Perhaps: Exercise for 30 mins. per day. Do whatever you need to to support whatever kind of exercise he chooses. Provide sports equipment if needed, or drive him to a swimming pool, or whatever it takes.
Then keep slowly adding positive goals. In this way, you will gradually reduce the amount of time he spends playing video games, just by filling up his day with other productive tasks.
Other goals to add:
Volunteering 2 hrs. per week, caring for a pet, do yardwork or specific housework, taking a class of some kind