Health and time are really what you should keep in mind, but I wouldn't get into real estate right now. I'd study and learn several investment vehicles - RE, equities, commodities, etc. So that when a great buying opp presents itself you're ready. In the meantime I'd suggest parking that $20k in an etf or two. Just remember to save early and often, compounding interest is what will make you rich, not yolo gains.

Get into sales. If you study and care, you can make millions each year, $100k is a minimum. I would say skip college though. The good thing about college isn't the degree it's learning to critically think and form opinions based on information you gather. I think many can develop this on their own but some do need guidance and college is one option. For people saying trade schools, it's an option, but start in sales, sell anything and study the craft, it really is an art. If you can get good at it the largest companies in the world will be fighting over you. It's the most useful skill in the world - not only to make money but influence decisions, friends and dating in particular. Understanding what matters to certain people and focusing on that is the key to life. Not working a house or fixing some ducting as some have suggested.