Charles P. Kindleberger is the Ford International Professor of Economics, Emeritus, at the Massachusetts Institute of Technology. He is the author of Manias, Panics and Crashes (Wiley, 2000) and A Financial History of Western Europe (OUP, 1989).

Advice on the percentage of equities that should be held in a portfolio varies. One suggestion is that it should be 100 minus one's age. For a 90-year-old, therefore, it should be 10 per cent. Elsewhere, a distinguished economist has said that the proportion of equities be the same at all ages.

What investments one should hold at 90 depends on one's time horizon, life expectancy, income, lifestyle, health, insurance, appetite for consumption, taxes, dependants, and needs and lifestyles.

To avoid taxation, one can reduce one's estate while alive by gifts to others and leaving money, tax-free, to charities. Some people buy life insurance in amounts needed to pay the tax, but for the very elderly the rates climb to levels roughly equal to tax rates.

Another tactic is to leave assets to grandchildren. These may lend them to parents. But loans within families must pay interest at close to market rates; if not, they are likely to be considered tax evasion.

A loan to a child to buy a house should use a formal mortgage, which becomes part of the estate. The inheritance of that person can include cancellation of the mortgage.

It has been suggested that people approaching retirement should shift to lower-risk investments. For the very elderly, investments with minimal risk are suitable, such as money market fund or certificates of deposit with maturities of less than a year.

Income is likely to be limited but the risk of dying in a financial crisis with losses in risky assets for heirs is broadly eliminated.