This is the 2562nd most frequent Japanese word.
定年
"定年" (teinen) means "retirement age."
In this sentence, '定年' refers to the official retirement age at a company or organization.
彼は定年を迎え、会社を退職しました。
He reached retirement age and retired from the company.
Here, '定年後' is used to indicate the period after achieving the retirement age.
多くの人は定年後に趣味を楽しむことを計画しています。
Many people plan to enjoy their hobbies after retirement.
In this usage, '定年制度' refers to the institutional system of retirement age in organizations.