I think I was better than most kids at math, particularly algebra, but those kids grew up and caught up and I suspect many of them are as good or better at math than I am. I know nothing about child psychology or anything adjacent, but I honestly think a lot of "advanced child" stuff is just maturity.
You should have learned roughly what is in this book at grade 7, it includes algebraic expressions, angles, ratios, unit conversions, statistical concepts like mean, mode, bar graphs, probability of dice and coins and so on.
https://archive.org/details/newenjoyingmathe0000jose/page/4/...
Then in grade 8 you'd go on to do those kind of things but a bit more advanced. Most people just forget how much math they learned and think they learned all that in high school.