Men, like women do have a biological clock. Men over the age of 35 the increase chance to conceive raises twelve percent and that percentage keeps increasing as they age. At the age of 35 it can take a man almost two and a half years to get a woman pregnant. Given that my prediction for you post-cataclysm are chance that you'll spend the last part of your life spread eagle in a tent trying to pregnant your harem. At least you will die with a smile on your face. lol.