Elderly Germans may have to keep working until the age of 69 if a Bundesbank proposal is adopted.
It says Berlin should consider raising the retirement age to that level by 2060, from around 65 at the moment.
The central bank says that otherwise the country may struggle to honour its pension commitments.
It points out that the state pension system is in good financial health at present, but will come under pressure in coming decades.
The Bundesbank says that as baby-boomers - those born in the post-World War Two period - retire, there will be fewer younger workers to replace them.
'Step by step'
The retirement age for Germans is set to rise gradually to 67 by 2030.
However, the bank believes that from 2050 this increase will not be enough for the German government to keep state pensions at their target level of at least 43% of the average income.
It is therefore proposing pushing the retirement age up to 69.
"Further changes are unavoidable to secure the financial sustainability (of the state pension system)," the Bundesbank said in its monthly report.
But German government spokesman Steffen Seibert said they stood by retirement at 67.
"Retirement at 67 is a sensible and necessary measure given the demographic development in Germany. That's why we will implement it as we agreed - step by step," he added.