I know some people who have to think about it for a few seconds.

I don't think I know anybody who flat out can't read them, but I know they exist.

I had a friend who had a watch that read in Ship's Bells.  I had a hard time reading it....correctly!  One bell every two hours??  Something like that.

My 13 year old step daughter.

We went on a cruise a couple months ago. I love cruises because that's a week stupid cell phones get turned off and thrown in the safe.

We were sitting somewhere waiting on something to start. Since her stupid phone wasn't glued to her hand she asked what time it was. A laughed and said "there's a clock on the wall right in front of us'" She said "I know but I can't read it."

I have no faith in her education. They are aloud cell phones, earbuds, drinks, food, gum, etc. during school. Granted there weren't cell phones in my day but everything else was prohibited. Her backpack is a vending machine, not a "book bag."

My buddy picked up one of these recently.

I'll admit, after my first brain surgery it took me abut 3 months to learn how to again but I can do it as of today

Not off the top of my head, no. My kids both learned in the first or second grade, I think. Something like that. 

Binary clocks trip a few people up, though. 

Yep, my wife has trouble reading analog clocks. She can, but she is ass slow about it, and if it's past the half hour mark she will often get the hour wrong. Her excuse?  "They didn't teach it in school." Well that's fine, but I assume that it is possible to learn things after one leaves school.

I have met other women that cannot read them. Not sure what the connection is, but the only people I've ever known that could not read an analog clock, were of the vaginal persuasion.

People that have a natural curiosity for tech and history will know. Most people don't.

I know only a few people that I would confidently say could be thrown back to the 1930s and still know how to start a car, tune a radio, and (apparently) find the time.