English grammar is heavily taught in elementary school (K-5, ~age 5 to 11) and middle school (6-8, ~age 11-14) curriculum in the US.
You're pretty much expected to have the grammar down by high school, where the focus shifts to composition (essay courses, etc.)
This was my experience growing up here anyways. The last time I had a test question ask me to circle the past participle was middle school (and the SAT).
Do 14 year olds in the USA know what "gerund" means?
I didn't know terms like that in England in the 2000s, though I picked them up from learning other foreign languages later.
I have heard university professors complain that they can say, simply, "rephrase the paper into the active voice" to a student from <anywhere else>, but many British students don't know what that means.
England now teaches more grammar, but it is not much use generalizing from individual experiences of a particular state/country in a particular decade.
No, I don’t think most 14-year-olds in the USA would know what a gerund is, but most of them would know active versus passive voice. Maybe the kids in advanced or hobbies classes, though. (Speaking as an American high school student)
You're pretty much expected to have the grammar down by high school, where the focus shifts to composition (essay courses, etc.)
This was my experience growing up here anyways. The last time I had a test question ask me to circle the past participle was middle school (and the SAT).