This is the 9055th most frequent Polish word.
starzenie
Aging.
The word "starzenie" is used here as a noun to denote the process of aging, specifically of the skin.
Starzenie się skóry jest naturalnym procesem.
Aging of the skin is a natural process.
In this sentence, "starzenie" describes the general process of aging related to the body.
Właściwa pielęgnacja może spowolnić starzenie się organizmu.
Proper care can slow down the aging of the body.
Here, "starzenie" is used to describe the demographic phenomenon where the average age of a population increases over time.