From what I’ve seen with other’s experience, he may have some arthritis which reduces his grip and agility. Adding branches or vines in between what you already have can be a help for him. Some have added safety nets to keep their falling chams safe from injury.
My old girl, also 6, has an occasional stumble of missing a branch, but hasn’t fallen. For the past couple of years, she hasn’t been able to shoot her tongue out more than a couple of inches, but she has a shooting gallery feeding station, so she gets right in there to get her bugs. She does pretty well catching black soldier flies even. I haven’t made any real changes for her, but I do watch her a bit closer and am prepared.
I have already decided that I won’t be putting her through vet visits for the natural decline and effects of aging, unless she is needing a humane euthanasia.
Best advice I can give and it doesn’t apply only to chameleons, is make the most out of every day he is with you.