So you decided not to go to college? No problem! Do you have a degree and want to expand your knowledge? Sure! As a man in my mid-30s, I feel some pressure to finish a degree (in biology), but I must remember that there are always ways to learn beside school. I am a committed lifelong learner, always have been, always will be.
And what better place to do so? The Internet! Whether you’re curious about history, geography, the sciences, money/economy, the arts, religion, literature, politics, you name it, it’s all there! One great way to learn such stuff is by viewing lecture notes from college course websites. And if you are ever confused, keep googling, and you can learn more and more about your topic. Many pages even have YouTube videos, especially in sciences. (These sources are not to be confused with online courses, which are complete, bona fide college courses that simply use the Internet as the method of delivery.). You can also use reference books (I enjoy an online subscription to Britannica as well as a printed science & technology encyclopedia made by McGraw-Hill. Steer clear from Wikipedia, though, their information could be shady.)
Yet, without application of such information, it becomes irrelevant, and thus faded. So should you brush up on previously known topics? That will depend on how much you use the information. It can be a waste of precious time that could be spent on learning new things. And in many cases, ignorance can be bliss!
King Solomon has mentioned in his Old Testament book Ecclesiastes, overall, that knowledge and wisdom can be tough to get and hold onto, and can be quite wearisome and insatiable. Of course, work, pleasure, and other earthly pursuits can be that way too. He’s not saying they’re sinful, but one must put God as head of them all. Also, everyone’s interests are different, so what one person likes may not for another. This is discussed in the New Testament letter to the Philippians: we should be humble and subordinate to others. This follows the “God-Others-You” paradigm: God first, others second, you third.
To sum up, knowledge (and wisdom) are there for glorifying God, not mere commodities for transmission and possession. Whenever you wish to share your knowledge, consider their interests, and as needed, explain it.
Here are some links to show information in a whole bunch of fields.