As already mentioned, the problem is more likely not enough protein. It is fairly impossible to overdo protein in the diet; if the bird is getting more protein than it needs for body maintenance, it can convert the protein to energy instead. (Although this is much less efficient than converting fat or carbohydrates to energy, plus protein foods are more expensive, so protein is not really an efficient source of energy to feed) There is nothing wrong with feeding things other than the bagged feeds, certainly, but just like people, they won't live that well on a "junk food" diet.
Commercial-type red sexlinks are not exactly bred for longevity. Their specialty is to lay a LOT of eggs in a short time, and it takes a toll on them. It's not unusual for them to look like old birds by two. They are not really intended as long-term laying birds, they are designed to be replaced every couple of years in a commercial henhouse setting. You can certainly keep them alive, laying, and healthy longer, but it's normal for them to get kind of yucky looking by that age.
I also agree on not giving them a heated coop. They are better off without it. They don't need a night light either. Chickens survived for a very long time without those things, and by using them, we are not doing the birds any favors; all we are doing is propagating weak birds that need to be babied to survive. Chicken feathers are great insulation (ever worn a down coat or slept under a down blanket?) and the birds will be quite warm even below freezing with no heat as long as they don't get soaking wet. Also, going in and out from a warm coop to a cold outdoors is hard on any animal, the frequent temperature change makes it take more work for them to regulate their body temperatures. Save yourself some money on your electric bill and turn off the heat lamp.
Commercial-type red sexlinks are not exactly bred for longevity. Their specialty is to lay a LOT of eggs in a short time, and it takes a toll on them. It's not unusual for them to look like old birds by two. They are not really intended as long-term laying birds, they are designed to be replaced every couple of years in a commercial henhouse setting. You can certainly keep them alive, laying, and healthy longer, but it's normal for them to get kind of yucky looking by that age.
I also agree on not giving them a heated coop. They are better off without it. They don't need a night light either. Chickens survived for a very long time without those things, and by using them, we are not doing the birds any favors; all we are doing is propagating weak birds that need to be babied to survive. Chicken feathers are great insulation (ever worn a down coat or slept under a down blanket?) and the birds will be quite warm even below freezing with no heat as long as they don't get soaking wet. Also, going in and out from a warm coop to a cold outdoors is hard on any animal, the frequent temperature change makes it take more work for them to regulate their body temperatures. Save yourself some money on your electric bill and turn off the heat lamp.