How to look at the age of gray swallows

As long as the age of gray swallows, as long as you look at its skin and feathers, the young bird's hair is bright, the skin is thin, the old bird's feather color is dim, it looks messy, and the legs and paws have thick leather.Raising this kind of bird must be picked. The young birds will be raised for a longer time, and they will better recognize the owner. The old bird is not good at judging how long it will live, and I don't know how long it can be raised.