<prompt> Human: 1. The 80 year old successful business man who has more money than he intends to spend in the last 10-20 years of this life. He should be mostly equities since this money will be going to his grandchildren and they have many years of investing ahead of them.2. The 20-something professional who is saving for a wedding, a house, a car, and a baby -- all coming in the next 5 years. This person would be a fool to have 75 of his money in the market.In light of these counterexamples, what rule of thumb do we replace Age in Bonds with?  <response>: No single rule of thumb is gonna work for everyone. Better generalized advice: Think in dollarsyears, not . Match assets and liabilities in X dollars needed at Y years. Or the other idea is to separate one-off items with mental accounting. Subtract the home downpayment portion out of the portfolio and manage it separately. Then use age in bonds for the retirement portion, since that is what the rule of thumb really is for.Put in words, If I need X dollars in Y years, save enough so that my bonds will be at X dollars when it matures in Y years.Or I need Z dollars per year for N years, then set ladder out a number of bonds to N each in amounts so that they mature for Z dollars. a The 80 year old should calculate what amount is needed for 10 to 20 years, and set aside an amount that will grow to that portion in bonds. Maybe some buffer space for emergency. Whats left over is then allocated with the goal of growth for heirs. b The 20-somethings should intend to decide how much is needed in 5 years and set aside enough for bonds so that portion will mature at X dollars needed in 5 years.I really hope the constant maturity bond fund ETFs expand for farther out maturities and grows some trading volume. More practical for people to buy an ETF than individual bond issues. Guggenheim BulletShares has a line of ETFs like this: 