Had a thought a while ago about the optimal age for females in a species to start reproducing and how it relates to the average age that they actually do start. Suppose there is some optimal age X to start reproducing that will allow the females to leave behind the greatest number of offspring. Females that start reproducing later than this age will leave behind fewer offspring on account of having a shorter breeding period until death or menopause. Those that start reproducing earlier than age X will also, on average, leave behind fewer offspring due to the greater risk of death during labour or other complications. Females that start reproducing at age X will, by definition, be the most reproductively successful and it must then follow that the average age of first reproduction in a species will stabilise around that optimal age X. I can't be the only person to have realised this so does this principle have a name in zoology or evolutionary biology?