I'm actually (re?)taking a math class (that I exempted originally) at the college where I am a professor now. What I'm finding is that the concepts of the class come back pretty quickly. What's taking a little longer is speed and precision. I'm slow and I make careless arithmetic mistakes. That's improving, but slowly, a month into the semester.
For me, it's been a little over thirty years since I've thought systematically about this particular branch of math if that gives you any kind of gauge, though I have used it here and there over the years, some parts more than others (and a few not at all - not surprisingly, they're coming back the slowest).