You know, actually, could it be possible that he has Cushing's disease? Please don't take this the wrong way, but he is pretty overweight and long curly hair like that is supposed to be an indication of Cushing's disease in horses. I hadn't thought about it until I saw these most recent pictures.
Here's something interesting I found when I googled it:
"Myth: Every curly-haired horse is a bona fide Curly.
Truth: They're not. Non-Curly horses with Cushing's disease have curly hair coats, too. Cushing's disease is caused by a pituitary problem. Afflicted individuals grow lots of long, curly, slow-to-shed hair that feels coarse and brittle to the touch, unlike a healthy Curly's fine, soft coat.
Horses suffering from Cushing's disease don't display secondary Curly characteristics such as soft, calm, heavy-lidded, almond-shaped eyes; small, crescent-shaped nostrils; proportionally short, broad, and shapely ears; and narrow, somewhat upright, hard and ultradurable 'mule feet.' "
That was taken from here, in case you're interested:
Dreamswept Farm - Articles - The Truth about Curlies
Maybe you should look into having him diagnosed by a vet? Again I don't in any way mean that in a negative sense. He's obviously well taken care of and happy from the looks of those pictures, but he certainly has the body type and, if I'm understanding correctly, age to be a Cushing's suspect. There's a lot you can do with diet and exercise to make an Insulin Resistant horse healthy again and I assume the same can be said for a horse with Cushing's.