Ginny O'Brien will not reveal her age. "Late 50s" is the most the founding president of the Columbia Consultancy, a Massachusetts-based executive coaching firm, will muster. It's a curious response from an otherwise straight-talking and driven woman who counsels female professionals aiming to climb the corporate ladder. Then again, O'Brien is in a good position to know that age discrimination definitely exists in the workplace. Almost 18,000 charges were filed in 2004, according to the Equal Employment Opportunity Commission (EEOC). Of these, around 41 percent were filed by women; the average age, 51.

Some industries are worse than others. "Women in broadcasting, cosmetics, consumer products, environments where you have to represent a certain look and statement to the public" are typically more vulnerable to being squeezed out as they get older, says Julie Goldberg, senior client partner at the global headhunting firm Korn/Ferry International. In advertising and public relations, "once you're past 40, you should be looking for another occupation," says Scott Kane, founder of Gray Hair Management, a Deerfield, Illinois, coaching firm. Much more age-friendly are professions such as law, medicine, and accounting, where experience and maturity work to your benefit, says attorney Lisa Klerman, a Southern California mediator in employment law cases.

No matter what industry you're in, though, it's never too early to start age-proofing your career.