Before now, my last math class was 20 years ago. Music degrees do not require advanced math classes. Therefore, I have not had a math class beyond the core requirement in all of that time. Is this a reasonable goal? Is attending math classes after so long that good of an idea? Well, that answer is complicated.
If you were an excellent math student 20 years ago and retained a good amount of your understanding, you will be able to resume classes exactly where you left off. The last math class I took then was College Algebra. The following math class in the sequence (for most degrees) is Pre-Calculus. I am enrolled in that now. I am not re-taking College Algebra. If, however, math was not your best subject, I do not recommend doing this. My reasoning for this is simple: while I am not having trouble understanding the material, it takes me a very long time to complete assignments. The lengthy assignment completion time is the result of my memory. I now must lookup formulas that others have memorized and re-memorize procedures that I used to know (for exams).