Don Ball is a 55-year-old engineer. According to mortality tables, a male at age 55 has an average life expectancy of 21 more years. Don has accumulated $48,500 toward his retirement. He is now adding $5000 per year to his retirement fund. The fund earns 12% interest. Don will retire when he can obtain an annual income from his retirement fund of $20,000, assuming he lives to age 76. He will make no provision for a retirement income after age 76 (i.e. he assumes he will be dead, nice thought, huh?). What is the youngest age at which Don can retire?