At 42 yrs old n I take min.6 hrs of sleep every night I still yawn a lot during office hours why?

Yawning. You don't have to be tired to yawn. Some people will yawn as a form of stress relief or as a habit.
More or better sleep. Try getting more sleep. Six hours is rarely sufficient for an adult. Getting by on insufficient sleep is like "getting by" on 800 calories per day - you can survive, but you won't thrive. If more sleep doesn't help, get evaluated for a sleep disorder.