An intelligent creature who's natural life span is around 50 years in which they need to feed to not die of starvation after which they naturally die.

  But killing other beings of their own species increases their lifespan... By how much? It does not matter, but it needs to exceed their natural death of old age.

How can such mechanism work in real life without magic?

There is an intelligent creature whose natural life span is around 50 years, during which they need to feed to not die of starvation, and after which they naturally die. But killing other beings of their own species increases their lifespan. By how much? It does not matter, but it needs to exceed their natural death of old age.

How can such a mechanism work in real life without magic?