Old for young otherwise referred in concepts of "enforced population limits" or "population management", is a theme or concept of a custom of human sacrifice —ie. where the old sacrifice for the sake of the young, either by self for sake of natural balance, or else by enforced law for sake of population control quotas. The concept is found typically within certain types of theoretical literature and science fiction stories, which may promote the concept as a means for ending enduring types of social conflict, or else deride the concept as utopian idealism gone awry.

The concept is somewhat in contrast with certain apparent modalities which underlie various types of current conflict. War, being the primary example, is infamously regarded as a sacrifice of the young for the sake of the old, (ie. where "old men send young men off to die"), or else a sacrifice of a particular demographic (ie. young men, low-income young people) for sake of another demographic (ie. the society at large, elite-income young people). Such may also have pejorative notions attached —the sacrifice of young belligerents for the sake of more civilised young people, etc.

Some notable examples include:

• Logan's Run - (late 20th century novel and film) in which all are mandated to be terminated upon reaching the age of thirty years. The dystopian theme is a Cold War allegory, asserting the nature of the "East and West" contrast as one of totalitarianism versus freedom, as these are manifest as artificial and natural drives, respectively.
• The "LifeDeath" story arc in the X-Men comic book — describing the practice of a fictional African tribe, in which the village elder, upon the birth of a new child, allows himself to die for sake of keeping the natural balance found by experience to be necessary for the tribe's survival.