The BMI chart
Age is only used for pediatric/young adults, often calculated to age 18 or so.
After this point, we only use height
and wt to determine healthy vs not-healthy-wt ranges for both men and women. It is a rough estimate and provide you a guide to keep "ideal body wt" for better health. If you have specific concern about your wt/height vs age (we shrink in height with age), consult doc. Good luck.