In my estimation, life in a stall takes its toll on any horse, but especially a senior. If a senior horse must live indoors, he needs regular exercise. In addition, dust and ammonia in the barn must be eliminated. Ammonia fumes, which are generated from decomposing manure, urine and bedding, are caustic to the respiratory tract of both horses and humans. Keep stalls clean and be sure the barn is well ventilated.
Many horses are happiest living on pasture.
For free-minded old timers, choose a pasture that has enough room to roam but not so much lush grazing that it leads to an unhealthy weight gain. No matter where a senior lives, provide a soft place for him to lie down for at least a portion of the day. As horses get older, they have less tolerance for temperature extremes. But oddly, many horses choose to stand out in a blizzard so you may need to provide a stall or storm blanket. During the summer, provide shade, ventilation and fly protection.