She's not elderly- in my book, until she has stopped laying, but she is an older chicken. I'm sure chickens, like any animal, have genetic issues with offspring and age but that may not be why your chick died (so sorry for your loss!). Sometimes chicks die. It's sad, but true. I lost 2 out of 7 this fall. One appeared to have choked. The other hatched with a wry neck and a week or two later, died. There may not have been a human or genetic cause for your chicks death. Chickens were breed to lay eggs or be meaty. They were not breed for longevity.
That being said, from what you shared, he may have been to young to be outside with the other chickens. I like to hatch my eggs with the mother and let her take care of them. Right now, for example, I have 2 large Rubbermade storage totes with the mother chickens and their babies in my house. One mother and chicks per tote. I don't need a heat lamp because the mother keeps them warm under her feathers. I have an old baby gate and window screen secured with a bungee cord over the top to keep the chickens in and the house cats out. One of the mothers laid an egg this morning, so I'm thinking she might be ready to go back out to the chicken coop. Her babies are a little older than the others. When the other mother lays an egg I'll put her out in the coop too and keep the babies all together in one brooder/tote. The high temp where I live right now are in the 30s so it's too cold for the little ones. Even if the weather was nice, I would not put them out with the other chickens- in general population, until they are almost full grown. I they are too small they will get picked at by the big ones. I have a corner of the chicken coop that I can close off to introduce new chickens, or to separate chickens that are getting picked on and need a break etc. I highly recommend every coop have one!
Best of luck in future hatchings! Don't give up, it can be heartbreaking, but it can also be wonderful!
~Emily