This is the 17137th most frequent Russian word.
старения
Aging.
In this sentence, 'старения' is a noun in the genitive case, used to specify the concept of aging as a process.
Процесс старения неизбежен для всех существ.
The process of aging is inevitable for all beings.
Here, 'старение' is in the nominative case as a subject of the sentence, referring to the aging process of the skin.
Старение кожи можно замедлить правильным уходом.
Skin aging can be slowed down with proper care.
The word 'старения' is used as a genitive form modifying the noun 'механизмов', indicating the mechanisms associated with aging.