Maybe it's time for me (40+) to go back to college. I want to pick up Mathematics and Physics up to the point of General Relativity. Since it's "use it or lose it", I better start reading now.

But I don't really have any time. There are so many things to do, to learn. Younger people who happen to stumble upon this reply, please please prioritize financial freedom if you don't have a clear objective in mind -- and from my observation many people don't have a clear objective when they are in their 20s! If you can retire around 35-40, you have ample time to pursuit any project you want for the rest of the life.