定年 (teinen) means “mandatory retirement age”

More examples

健康であれば、定年の後も新しい仕事を始められます。ken kō de a re ba tei nen no ato mo atara shi i shi goto o haji me ra re ma su

If you are healthy, you can start a new job after the mandatory retirement age.

Refers to the age set by an organization as the point when an employee must leave regular employment.

退職年齢taishokunenrei: The age when employment ends, without always implying a mandatory rule from the employer.

組織が定めた、職員や従業員が通常の勤務を終えて退職する年齢。so shiki ga sada me ta shoku in ya jū gyō in ga tsū jō no kin mu o o e te tai shoku su ru nen rei

定 (tei, "fixed") and 年 (nen, "year") combine in 定年 (teinen) to express an established age for ending one's employment.

A workplace can have a 定年 (teinen) even when an employee continues working afterward in a different role or under a new contract.