Alexis,
If you are already looking at RE at 21 you are well on your way to financial success. As Brian mentioned, getting your RE license would be a HUGE start to. That gives you the opportunity to network and please do network all you can. As a new RE agent lawyers, bankers, title companies, accountants will all give you there time FOR FREE, or at least that has been my experience, to potentially get your business down the road.
It may not get you your first deal, or it just might, but it will at least give you a solid base you need to move forward with deals once you actually find them.
Then actually selling/buying places as a Realtor will get you first-hand experience with transactions. You can also, and it is recommended, to sit in on closings. If you hear of some creative closings, try to sit in on those as well.
As you grind along as Realtor you will come across deals that you might be able to parlay your commission into a piece of the project (commissions can really add up). Or you could have some cash saved and not only parlay your commission but add in your own capital to make it happen for a larger piece of the pie. Or just put the cash in and collect your commission at closing like usual.
Keep grinding but always keep reading and adding new strategies to your tool belt. If you find a strategy that works, mine the **** out of it but me mindful to keep learning and exercising other strategies so that you are more diversified and well rounded.
Just some food for thought.
PS. This is the route I took and it has snowballed.
PSS Patience, Persistence, & Perseverance is needed in RE.