Genuine question: at what age is Olber's Paradox explored in high school physics these days? (It was part of my A-level physics curriculum in the UK, age 17, circa 1981 ... I'm finding it rather odd that it was unfamiliar to this journalist!)
The physics courses I took (in both high-school and college) didn't generally deal with astronomy. Not sure how common that is. Instead they covered mostly "foundational" topics: general & special relativity, electricity & magnetism, mechanics, atomic structure, etc.
I think your experience is pretty typical. I had the same. I took what was technically considered a college-level physics course in high school, and we never really delved into astronomy. Only in college itself did the subject start to come up, and that's because I selected those classes.
I suspect this is because the US high school education system has a fairly standardized, one-size-fits-all curriculum. There are some allowances and exceptions, of course. But, for the most part, everyone is going to be covering roughly the same material. And astronomy isn't deemed as necessary, for the beginner, as some other rudiments of physics. College, on the other hand, offers more opportunity for individual choice in one's curriculum.
I had the same situation in college as well, though that could be because I went to a somewhat unusually set up science/math uni (hmc.edu), in which all majors had to take a science/math "common core". There were 3 required physics classes for non-physics majors, which were these, going pretty in-depth into physics but still not covering any astronomy: http://physics.hmc.edu/course/3/, http://physics.hmc.edu/course/46/, http://physics.hmc.edu/course/4/
Astrophysics is generally popular among students, but afaict it hasn't been included basically because the physicists consider the above three courses to be higher priority.
It wasn't taught in any of the physics classes I took in the US circa 1990. As a matter of fact, I hadn't heard about it (by name) until watching a Jim Al Khalili documentary from the BBC. I suspect that proper treatment of the subject would have offended those in the US that still believe in the firmament of heaven.
(I'm only partly joking. My high school biology class had a chapter on evolution. The teacher said "I have to teach this but I won't be testing you on it. Read the chapter and let yourselves out when the bell rings." He then left the room.)
I think that that "UK" makes quite a difference. In my experience, British education focuses more on historical and philosophical (aka 'impractical' :-)) knowledge than that of most other countries.
That experience is heavily colored by watching University Challenge and Mastermind, but I do not think that makes a difference when comparing the top levels (which, I guess, we are; those not in the top levels at A level physics will not remember hearing about Olbert's paradox)
Why unfortunately? They can hardly cover everything! And they certainly can't mention everything covered in the syllabus.
Typically it would be discussed in the context of cosmology; if they don't cover cosmology at all that's unfortunate, but not mentioning this very specific footnote to it would be understandable. And even if they do plan on covering it, I'd be a little surprised if it was listed on the syllabus.
