I give Blue SmartFlex Senior by SmartPak and its amazing. He's a very big bodied appy (17h, 1300lbs) and it does wonders for him, so if you're looking for a supplement, that's one I suggest looking into.
Blue taught me how to ride. He hadn't been ridden in a solid 2 years when I went to look at him. We saddled him up and I rode him (terrified out of my mind!) in a huge field with other horses running in a pasture near by. Blue never paid any attention to them and has carried me safely through many, many adventures, although he hates creek crossings ;)
The old ones are the wise ones and deserve a loving home in their last years because frankly, they've earned it.