Middlescence is defined as the time between adolescence and senescence.
"It is a paradox of life that we do not begin to live until we begin to die. Death begins at thirty, that is, deterioration of the muscle cells sets in."
From the video below: Life begins at 40: the biological and cultural roots of the midlife crisis | The Royal Society. In this lecture, Professor Mark Jackson, winner of the 2018 Wilkins-Bernal-Medawar Medal, explores a rich range of historical sources to argue that the midlife crisis emerged as a result of demographic changes, new biological accounts of ageing, and deepening anxieties about economic decline, political instability, rising level of divorce, and the impact of family breakdown on social cohesion.
Watch the Q&A here: https://youtu.be/q9erYW2KsUg