A sentence in my textbook is:
The possibility of female being haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life)
I know that haemophilia is an X-linked recessive disorder. Hence mother should be carrier and father must be affected for daughter to get affected. But I'm unable to understand what "unviable in the later stage of life" means.