In Ayn Rand's book Anthem why were men only expected to live to 40 years old?

-Because Rand pictures a Dark Ages, medieval-like dystopic future as opposed to a commonplace gadget-bound chock-full-in-technology future. She foresees irrationalism and collectivistic policies as sending humanity back to some sort of feudal times. This means going back to illiteracy, scientifically wrong beliefs (Earth is at the center of the universe, etc.) and rebooting health care and medical practices which nowadays enlarge our lives but back then couldn't keep a person alive for over 40 years (with great difficulty, of course).