As far as employment is concerned, as people take their pensions at the age of 65 at the latest, new staff cannot be recruited.

at 是介词，表示"在...时间点"或"在...情况下"。 the 是定冠词，在这里特指"最晚的那个时间点"。 latest 是形容词 late（迟的、晚的）的最高级形式，表示"最晚的"。 at the latest 是一个固定短语，意思是"最迟、最晚"，用来强调某个时间点是允许的最晚期限。