BMI does change with age.
More Info: According to a study published in BMC Public Health, significant increases in BMI occurred as the study participants—both men and women—aged.
Researchers from the University of Oslo in Norway set out to study individual trends in BMI in relation to age, gender, and socio-economic status over an 11 period. 1169 adults of both sexes participated in the study from a variety of socio-economic backgrounds. The research concluded that for women the proportion of obesity increased with age from 4% to 11% and for men from 5% to 13%. Socio-economic status did not appear to play a significant role, but the majority of the weight gain appeared to occur in young adulthood.
Inconsistencies with the BMI Index
The Body Mass Index scale does not take into consideration age or gender causing some professionals to disregard it as less than accurate. As an example, an athlete with the same BMI as a non-athlete tends to have more muscle mass than body fat. An older person with the same BMI as a younger person will tend to have more body fat. When measured for the exact same BMI women tend to have more body fat than men do.
Reas, Deborah L , Jan F Nygård, Elisabeth Svensson, Tom Sørensen, and Inger Sandanger. “Changes in body mass index by age, gender, and socio-economic status among a cohort of Norwegian men and women (1990–2001).” BMC Public Health 7.0 (2007): 269. Print.
“Healthy Weight: Assessing Your Weight: BMI: About Adult BMI | DNPAO | CDC.” Centers for Disease Control and Prevention. N.p., n.d. Web. 3 Oct. 2011. <http://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html>