If the promotion channels can stay smoothly open, then there will continually be new people coming up from the bottom levels, and people will be continually retiring from the upper levels, so there won't be a problem of aging and ossification.
假如公務人員升遷的管道能夠暢通的話，一方面經常不斷有新的人從基層補充進來；另方面經常不斷有人從高層退休，就不會發生年齡老化的問題。