A cohort means a group that shares characteristics, in this case, a group of the same age range, given that is about age, highest cohort could mean the group with the highest age (95-99) or the group with more members (50 - 54, 3.5%).
With the information we have, we can see that the birth rate has been consistent over the last decades, given that all the cohorts have approximately the same quantity of members (around 3%), which also allows us to see that the deaths occur from 60 years up, with the least of the population being in those cohorts.
The percentages of how many individuals are in each cohort could be modified by immigration because the cohorts to which the new individuals belong would have more members, with an abrupt change in the percentage, compared to the previous and next cohort.
Lastly, seeing the pyramid we can notice that, apart from the elder cohorts, almost every cohort has the same percentage of members, making the shape of the pyramid more like a barrel. This kind of demographic pyramid indicates a developed population because it indicates a stable and low birth rate, with a long life expectancy.
