Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 207 / 4 / b / i / Solution

The professors enter observation only when elected. Anyone dying before election cannot appear, so the birth-to-death sample is left-truncated at varying, outcome-related ages and is not an inception cohort from birth. Every listed professor was elected before age $60$ and survived to $60$, so all six are under observation from the common origin age $60$. The data can therefore estimate survival from age $60$ without delayed entry.