My precocious 5th graders always feel very sophisticated using these and understanding the meaning of the symbols. I don't think I'd go much lower than 4th grade unless the children are extremely advanced; but it's definitely suitable for older kids.
The male symbol represents the sword and shield of Mars. The female symbol is Aphrodite's hand mirror.
I print out a batch of these each year and laminate them, punching a hole at the circle up top and cutting down the line, hanging them off pus