Treating Real Estate investing as a business means different things to different people. The obvious one for me is that you have to plan. A hobby is something you can do on the side and whether or not it succeeds isn't of import, another way of saying to half*** it.
Treating something like a business is through your actions rather than your words. If you've got the drive to succeed, go out and meet real estate investors in your area. Start studying your local market, start studying for your Re license, devour every book, blog, or podcast you can get your hands on. Most importantly is your plan. Where do you want to go, why do you want to get there, how will you get there are some important questions to ask yourself. You have to be persistent, consistent, and disciplined in what you do.
Be a do-er rather than a talker. A business plan is also very important as well. Your livelihood depends on a business but a hobby is for fun without the risks.
Anyways, you have come to the right place at bigger pockets especially at such a young age. Best of luck to you and your investing future.