Do you judge players superficially before you get to know them based on their physical characteristics? I do and it's probably a bad habit.

Yesterday I was at a table where there were 5 aggro elderly persons (1 female). I couldn't believe it. The place I normally play at, "OMC" is an accurate term for the morning crew. They tolerate me because I'm not a wild man. The first orbit yesterday I was shocked at what was going on. I folded the idiot end of a straight to a raise and a reraise. It turned out it was top pair TK vs. top pair moderate kicker, lol.

VPIP and PFE are probably the best measures to keep track of in your head, but do you focus on physical elements for unknown players live?

I’m not so sure prejudice is the right word. It’s human nature to make snap judgements of others based on a number of characteristics. We assign these judgements from our past experiences. This, of course, causes us to stereotype others until proven otherwise. My experiences, like yours, have been that older players tend to be tight. So if one started being hyper aggressive, I would be surprised just because it is in incongruent with past experiences and assumptions we make based on stereotypes. I think everyone does this whether at the poker table or not.

People definitely overemphasize race. For example, read Jonathan Little's 1st cash game book, where he devoted an entire section to this topic. It's packed w/ all sorts of dubious nonsense about what assumptions you should make based on race. For example, I play amongst a very nitty player population that is mostly Asian. Yet the stereotype is that Asians are "crazy gamblers". Whatever. To quote Wolfgang Paulie, it's not even wrong.

Like you say, frequencies/showdowns are king in categorizing players. However, as far as physical indicators that might help me out immediately, I usually look at buy in amount, how they stack/handle chips, age, how they're dressed, how they hold themselves, how hard they seem to be paying attention, etc.

I used to argue with a Korean player who was our "house pro." House pro was what i called him. I thought he was an awesome player. I'm inclined to agree with you, but I'll tell you what he said, "There are only two kinds of Asian players--Gamble Gamble Asians or tight complete nits."
I said, "that's not true."
He answered, "It's absolutely true! Shut up. I know."
He gave me a laugh as he often did. Great guy.

I don't disagree with your main point but Little actually says Asians tend to be either wild or tight.

As to the main question of the thread, I don't think for most players there is any prejudice involved in making guesses about how people play. It's stereotyping certainly. And I do use all kinds of stereotypes to help me form a baseline when I have no actual information to go on.

One should take a complete inventory of a person's appearance and behavior, however, not just make conclusions like "woman = passive" or "black guy = loose".

Some stereotypes are obviously useful. If you treated OMCs like 25 year olds you would get murdered long term. OP's experience is aberrational. Of course various individuals differ greatly in their play from how their stereotypes depict them, which is why watching how people actually play is more important than just lazily using stereotypes.

But there are many times where I simply have no hand history with the individual involved. Rather than treat that person as a blank slate, I make an educated guess about his or her tendencies based on how other similar looking or acting people have played.

Some stereotypes I've found useful

Conservatively dressed - relatively tight or someone trying to appear tight

Shabbily dressed - gambler

Well groomed - tight

Unkempt appearance - gambler

Stacks chips neatly and correctly - tight

Stacks chips oddly or messily - loose, probably aggressive

Has a backpack - grinder

Wears sunglasses in low stakes games - inexperienced with hiding tells, probably bad

Young - relatively aggressive

Old - very tight

Middle aged - usually loose passive

Has non-American accent - relatively loose

Heavy smoker - relatively loose sometimes aggressive

Drinking - relatively loose

Heavily drinking - loose and aggressive

Talking a lot - loose or trying to appear loose

Silent - tight or trying to appear tight

Buys in for minimum - usually bad, could be aggressive short stacker or LP trying to hit a HH

Buys in for maximum - relatively good OR relatively wealthy gambler, can often figure out which by other appearance and behavior clues

Wears eyeglasses - probably intelligent, likely relatively good

I also use racial stereotyping but I'll avoid posting these as I don't want to offend anybody.

The correct way to implement stereotypes is by taking everything in, not just one thing like race, for instance "older black guy, conservatively dressed, chips stacked neatly and correctly, has not said a word, bought in max 200BB" is very different than "young black guy, loose fitting casual clothes, drinking, talking to his neighbors, chips messily stacked, bought in 100BB"

With no additional information I'm guessing the first guy is a nit and the second guy either LAG or SLAG.