With increasing life expectancy, the definition of "old age" also progress.
In early to mid 20th Century - 30 was considered "middle age" and 40-50 as "Old age". Now this is extendended by at least 10-20 years. Now, this is extendende by 10-20 years - 30 is "young" and 50-60 "middle age". In HK, "Senior Citizen" ("old") is officially started at 65 - and even this is probably too early. 70-80 is probably the real start of "old age". However, the retirement age is far lagging the life and health expectancy of people, and this is the real cause of so-call "ageing" problem - people are forced to retire at 55 - 60, which is the prime of people with normal health.