Even though I didn't grow up in a tech-savvy household and couldn't code my way out of a paper bag, I had one big thing going for me: I looked like I was good at programming.
I admit I've had predisposed biases about people before getting to know them. It's human nature, it's the way our brains work. The world is a complicated place and our brains need a way to quickly categorize what we experience or else we would be overwhelmed.
As a hiring manager, it's a part of my brain that I try to shut off when I'm assessing someone's technical skills--but it's tough. I've even played games in the past where I covered up the person's name before I reviewed the resume to see if that altered my impression of them. But over the years I've encountered enough individuals that violate any kind of stereotypes I had that it's unwound most of them.
People always talk about race bias and gender bias, but something that surprised me when I first encountered it (in myself and others) was experience or education bias.
Tess Rinearson in this article talks about the "technically entitled," the programmers that boast about how they've been programming since they were 6. You would think that someone who has been coding for that many years would be amazing, right? In my experience that's not always the case. I've had candidates tell me on the phone they've been doing C++ since they were in middle school but when you dig into it they can't answer simple questions about the language. Me personally, I started coding at a very young age but I know quite a few people that didn't start until they were in college and they are way better software engineers than I am. If you assume there's a correlation between experience and ability you could run into trouble.
What's especially surprised me talking with and interviewing folks from different colleges and universities around the country is its dangerous to assume there is a correlation between education (school and/or GPA) and programming capability. You would think Stanford has an amazing computer science program, being in the heart of silicon valley. Anyone with a Stanford CS degree must be amazing, right? Well... I've interviewed Stanford grads that could not explain some of the most basic concepts about how an operating system works. But I've also interviewed Stanford grads that during the interview taught me new things about how operating systems work. So you can't infer anything about ability from education either.
Race, gender, experience, education.. what inferences can you make about people then? None, really.