We have a 20 year old QH gelding. He has scar tissue and a dropping pastern from a bowed tendon when he was 14 -though he improves with exercise and stiffens when sedentary. He loses ALL of his hair each November for a few weeks before growing in a healthy plush winter coat (for the last 3-4 years). He used to be an easy keeper, and is now more of a normal keeper. He has lots of energy and will overdo it if you let him (we don't like doing high impact/high speed with him because of his old injury) - he used to be a barrel horse and is clearly an adrenaline junky.
We also have a 20 year old fjord/shetland pony. Her problem is that she has a fat neck, is over at the knee, is very stubborn with the kids, and requires almost NO food to remain fat despite regular exercise.
We love her though