When controlling for other factors (like age, weight, etc.) a paper found that there is no real difference between the metabolic rates of men and women.
The study also found that metabolism in women does not decrease with the onset of menopause as was previously thought.
Read What We Think We Know About Metabolism May Be Wrong from the NY Times.
Links to this note
Metabolism differs primarily in four distinct stages of life. From infancy to age 1 metabolism accelerates to 50% above the rate of an adult. From age 1 to 20, metabolism slows by 3% per year. From age 20 to 60 it holds steady (although people gain an average of 1.5 lbs per year in adulthood). At age 60 there is a 20% decline in metabolic rate by age 95.