Luxembourg's pensioners are among Europe's youngest and wealthiest, with the average retiree aged 62. The country managed to sustain the minimum pension of €2,351 thanks to a constant influx of foreign workers. But the party may soon be over. As population growth stalls and the pension reserve fund drains, prime minister Luc Frieden is borrowing a classic from Europe's playbook: raise the retirement age – by three months every year.

Even the wealthiest countries can't escape the math. By 2040, Denmark's residents will have to work until their 70th birthday, Europe's oldest workers. Since 2006, the retirement age in Denmark has risen automatically with life expectancy. Recently, social democrats have started questioning this law.