The first time I was told about syntax was when I was 12 or 13 years old, and I understood absolutely nothing: not even the subject and the predicate.
Seriously: nothing is nothing. Not even about what is not the subject is the predicate.
I owe a lot to my Spanish teacher when I was 15-16 (María del Mar was her name) for making me understand syntax.
Not only did I understand it, but I was great at it! I was at the top of my class!
Could it be that I suddenly became very smart, or, rather, that she was the first one who knew how to explain it properly?
(It’s true that, in my opinion, syntax is a bit too abstract for a 12-year-old).
I am going to say something unpopular among language teachers around here: much of the syntax that is explained in secondary/high school is, in my humble opinion, unnecessarily unnecessary: lots of little things, lots of little boxes, lots of little lines, lots of little labels.
Moreover, the concept of predicate, although linguistically correct, etc., seems to me to be completely useless in practice (for this purpose).
In my opinion, the useful and necessary syntax is much simpler: subject, attribute, direct and indirect object, regime complementizer, predicative, adverbial… and not so much more.
In my years teaching Latin (and syntax) to Spanish-speaking students, I have seen a lot of unnecessary syntactic trauma.
If you or someone you know has suffered any trauma with syntax, this link with text and video might help.
P. S. Really, no need to suffer with syntax. It can be even fun!