A very salient point. One, if you still have it on your resume, when you graduated from college. Most people my age have removed graduation dates.

Two, by your work history. Some people chop of everything but the last 10 years or so, which I have NOT done because all my jobs for the last 17 years have been in my field.

Three, the interview. Even people that dye their hair can't always pass ass younger.

All points are hot topics of debate though!