I have never had birds die that young. If your birds pass at that young of an age, something is wrong. A 2-5 year old silkie is not old. Some of my males do not reach sexual maturity until almost two, silkie males can be slow. I had a cochin bantam male live to be over 14 years old, and was still showing a gray silkie hen at age 8. She is retired now and is doing very well at age 9. I have several silkies that are over 9 years old. I would imagine it may have something to do with what breed you are raising, but I have had several breeds and never had any to die that young unless they had a health issue or went egg bound. So, if there are no unforeseen health problems your birds should live a long time if given the proper care.