> What you think and what you do, how you were raised and how you were educated -- these often matter far more than age and gender
But age and gender have huge effects on what you think and what you do, how you were raised and how you were educated.
To name just one example: because of Title IX, women who went to school in the U.S. prior to 1972 (tens of millions of people) had fewer opportunities in various sports, clubs, committees, activities, and even academic programs, than women to attended school in, say, the 1990s. These differences during childhood have produced differences in the careers, personalities, mindsets, and expectations of women of different generations.
This is just one specific difference in childhood that plausibly leads to different adult outcomes based on age and gender.
I haven't seen you provide any specifics. Instead what I see is vague pablum that reduces to "all people are different and each individual is unique." While that is true to some extent, by itself, that sentiment does not acknowledge or engage with the very real differences that people alive today experienced during their lives, based on their age, gender, race, ethnic background, nationality, etc.
> This is why people should be judged by the content of their character.
See, the problem is that you come out of a particular narrow formative experience too, which has affected your ability to neutrally judge the content of a person's character. You're not alone; it's true of everyone.
That's why looking at measurable diversity is important. The accusation that it's racist is beside the point; everything about human society in 2018 is affected by age, gender, race, etc. Intentionally and consistently considering diversity is how we consciously address and compensate for what would otherwise be hidden or unconscious bias and rejection.
You are right that mental factors matter most. But different mentalities are impossible to measure directly, and impossible to intuitively understand, because we are each limited by our circumstances. We know that different mentalities arise from different circumstances, so we must consciously consider a diversity of circumstances.