I don't know of any reason an older person could not take the SAT but also most older students interested in going to university would be admitted under different critera than a 17 year old, and high school grades and SAT might not be relevant at all for someone in his 30s or older.
Check out Barbara Oakley’s Coursera course called Learning How To Learn. It turns out exams are actually an excellent tool for learning, more so than learning without assessment.
A side effect has been that having a deadline and a measurable outcome has been incredibly motivating. I’d have probably been distracted by side projects if I hadn’t committed to the exams.
And yes, it’s accepted for uni entrance here. STEM courses at top unis will expect A-level grades in maths/science subjects, even for mature students with industry experience.
I’ve found having formal exams to study for very motivating, and humbling. I thought I knew things I’d read in books, but it turns out I just recognised them when I came across the same topic again. Being able to recall concepts and use them without help under time pressure is a different level of mastery.
Can you sit high school exams as an adult in the US? There might be private exam centres in a city. That way you’ll _know_ you’ve learned the math(s) you need, on top of all the great learning resources linked here.
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Edit: Cambridge International do A-level exams, with centres accepting private candidates globally: https://www.cambridgeinternational.org/programmes-and-qualif...