How does an elderly substitute teacher get the respect of their temporary class?

I am an elderly woman who does substitute teaching. I cover all grade levels and all subject matter. After two years of working with students of all age groups, I still have not been able to get respect from more than 3/4 of a class. If I'm nice, soft spoken and lay down the rules of the classroom, that doesn't work. If I am stern, mild tone and lay down the rules along with consequences for misbehaving, it doesn't seem to work either. It just seems that elderly women are not respected, especially in middle school and ocassionally in all grade levels.