@Jero, for officials that have positions that span multiple tenures then they will contribute to the data for the different tenures. The age displayed in the box plot is the age of the position holder at the beginning of the tenure. For instance, say a candidate called Jero born 1990 was HoR for 2015 and 2019 tenure, then they would be registered with age 25 and 29 for the 2015 and 2019 tenures respectively.

Thanks. This address my question.