IMO he needs more weight. Have you read his teeth? I see an older horse in the front of his legs (skin sags), the sinking above his eyes, the lack of weight behind his forearm,
And his back--here is a picture of my high withered 6yo KMH for comparison
I keep Him on the slim side bc the TWH that I bought as a 19yo died of Cushing's disease at 24yo, and he's a big guy (16'3hh.)
Teeth tell a horse's age. Here's what to look for:
reading a horses age by teeth - Bing Images
THIS picture of of a 14yo horse's teeth, for reference. Galyvayne's groove has travelled about 1/2-way down (or up) from the gums.
An 11yo would have just a little stain starting at the gums. A 20yo will have the full line, to to bottom. After 20 years, the groove begins to recede, until age 30, but by then the horse does look old.
I think your horse is about 23yo.
I'd be happy to be wrong.