The man broke into her home during the night and said: "I am 80. Give me your money," according to the Tokyo Metropolitan Police.

The woman then grabbed a heavy glass ashtray in an attempt to fend off his knife, but the aged robber still managed to get away with 50,000 yen (about $416).

Some commentators fear that this robbery could be the start of a "grey on grey" crime wave, as Japan struggles to support its rapidly aging population.

The robber, who is described as a man in his eighties, broke into the woman's home through a bathroom window at around 1.30am on Friday.

Although he had a knife, the elderly lady was still determined to defend her possession when she hit the robber with the ashtray.

"I tried as best as I could to strike back," she said.

Aging Japan Average female life is 84.93 years Male life expectancy is 78.07 years 17,394 people over the age of 100 84% of centenarians are women

Police said that they were unsure why the man told her his age.

After taking the money from a wooden box, the man escaped out of the back door, leaving the woman with a slight cut above her eye.

The Japanese have the longest life expectancy in the world.

Their diet of fish and green vegetables are thought to contribute to their longevity.

Whilst Japan's high proportion of elderly is testament to its society's healthy diet, the greying population places a heavy burden on Japan's pension system.

Some now fear that the financial burden could be accompanied by a rise in elderly crime.