When do you become a senior citizen?
That's an increasingly important question in Japan, demographically the world's oldest nation, where the challenge is to keep people healthy and productive as they live longer.
The answer should be 75, 10 years older than many people think now, according to two groups of medical experts who specialize in aging.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.