IQ is age-adjusted. Without the adjustment, it drops quite a bit.

Some cognitive abilities diminish more slowly with age (so-called crystallized intelligence), but unfortunately, fluid intelligence drops noticeably much earlier in life than most people would care to realize.

You just need to lean into what you know instead of solving novel problems. Or be comfortable knowing that it'll take longer than it used to. Typically, you can still arrive at a solution if you could have before, but you'll need to put more work into it. Sometimes, a lot more work.

- A homeschooling father helping with SAT prep