When do you think you'll retire? Aged 65? Younger, if you're lucky? Maybe older if you're unlucky—or if you're young right now?

Someone from a high-income country starting their first job can expect to retire on average two years later than today's pensioners. And in some countries the retirement age will be much higher. Denmark is planning on raising its pension age to 74 by 2070.

Yet despite all the changes over the last 70 years in society, job markets, educational systems and retirement policies and trends, the working age as defined by the wealthy countries of the Organization for Economic Cooperation and Development (OECD) is still 15 to 64.

Having a defined working age helps individuals planning their retirement as well as governments making spending plans. But it's puzzling that this age bracket remains the standard measure.

After all, a large number of people outside this age range continue to contribute to the economy in both formal and informal ways. Even with today's pension ages, in OECD countries an average of 23% of people aged 65–69 are still working.

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