I was forwarded an email today from a 60-year-old man in China who said he dreamed of studying in the U.S. when he was young.  Now that he can afford it, he wrote, he is too old, but he still holds onto his dream.

It was such a sweet email, so I started looking through the State Department website to find out whether someone who doesn't need a degree and isn't really college age could still fulfill a dream of studying in the U.S.  And I found this:

If you are going to the U.S. primarily for tourism, but want to take a short course of study which is recreational (and not for credit towards a degree), and the course is less than 18 hours per week, this is permitted on a visitor visa. As an example, if you are taking a vacation to the U.S., and during this vacation you would like to take a two-day cooking class for your enjoyment, and there is no credit earned, then this would be permitted on a visitor visa.

Turns out,  some universities even explicitly make courses available to international visitors who want to do some recreational studying during their trip.  Take a look at Boston University's webpage about summer semester courses.  BU recommends that all students pursue full degrees under F-1 status, but says:
If the main purpose for being in the country is travel or tourism, you may take one course at Boston University during the summer.

Many older Americans will audit a course at a university to enrich their knowledge and pursue their interests, and it looks like someone traveling in the U.S. may be allowed do the same.

If you're thinking about doing this while on your vacation in the U.S., be sure to check at the US Embassy or Consulate in your country to find out more information - we're not immigration lawyers here, just information-sharers.