My Lacey girl is turning 28 in the spring! As far as "special needs" go, my girl's only major special need is that she's mostly blind due to ERU (Moon Blindness) so she needs special things (limited mud, she gets "stuck" sometimes in her pasture and can't find her way back to where she wants to be so she's stalled at night to prevent that sort of thing, doesn't do well with other horses, etc) that way. As far as limitations due to her age, I haven't come upon any yet.
I mean, she is much "easier" to deal with than a younger horse since she pretty much knows the rules, she's not too interested in just making trouble, that kind of thing. However, she's never had her full vision in the time I've had her (I "rescued"/got her when she was 23) so I'm not really sure how much is vision-loss related behavior and how much is just her.
I do blanket her when it rains, at night, and when it's below 40*F since her ERU can be triggered by getting chilled and because...well, she deserves the cushy life!
I don't feed her anything special, she does have insulin resistance (like diabetes, for horses) so she is on a low starch-low sugar diet. She gets a pound of alfalfa pellets in the morning and a pound at night mixed with 4 oz of flax seed (they help her eyes and make her coat really soft) and 2oz MSM (also for her eyes but helps with her joints too), soaked. And she gets free-choice grass hay plus 5lbs of alfalfa per day. She has all her teeth so the soaking is really just to make sure she actually eats her supplements. She also prefers it soaked so who am I to refuse!
Her "thing" is being stupidly obese all summer, then dropping weight like crazy in the winter. So she wears a grazing muzzle all summer plus no hay (her pasture is more than sufficient in the grazing department) and as few pellets as possible to get her supps in her, then in the winter, she gets lots of pellets, lots of hay, and alfalfa. The alfalfa in the "ticket" to keeping weight on her in the winter - every other solution just fails.
I think the worst part of owning an older horse is the question of when they'll go. I adore my girl and I can't imagine my life without the old lady but I know that at nearly 28, ten more years is not super likely. And that's hard. At the same time, knowing that, every morning I see her gallop, bucking, out of her stall is all the more special.
I figure that if she can have that much exuberant joy, who am I to complain that my train is late or that I didn't get an A on a test. WHO CARES, I'm alive and that's the best thing ever!