Your clock is ticking=social construct?

A lot of people (mostly women) talk about how they feel their clock starting to tick when they reach a certain age. Maybe it’s 30, 35, 40.

Obviously we all know there is a biological limit on when people who are assigned female at birth can give birth. But usually this occurs in the 40s, meanwhile I’ve heard young women in their 20s say they “feel their clock ticking”. In their case, they could have 20 childbearing years left.

Is the feeling of “your clock is ticking” due to social pressure, or is it biological? Have you experienced this feeling?