I've some 1.5million points on Khan in Math alone.

I would go back a year or two and do the Unit Tests. The final tests at the end of every unit. There might be, say, 8 - 12 of them in total. Followed by a Course Test.

From that, I'd see how many I got wrong and improve on them.

After doing all that, I would then see how I felt about picking a math subject.

As for me, I literally started from the bottom. I do not pick subject to learn. I just follow the coursework starting from Grade 1 to 2, 3, 4 and so on. Doing every exercise. This has orked for me, but my way is different from your indicative way of picking a subject your interested in. So my advice might not be the best.

Your advice is pretty good Oscar Sheen
We can be study buddies! I'm doing 7th grade right now. 

Thank you oscar.sheen. Yes, I definitely do go through the whole path. Partly because I have no idea what I don't know (which turned already out to be some), and partly because I'm just wired in a way that I have to understand and accomplish everything about a subject. A reason why me and school never hit off back in a day. If I don't understand everything, I feel like I don't understand anything, and it makes me anxious. So I just zoned out in school. 
I was always very interested about everything, but the school system really crushed me. I learn so very differently comparing to most. 
I'm only about to finish 3rd grade soon, but me being me, I need to already have a path laid down in front of me. 
When watching the Courses list in math (post 8th grade), I really don't know are those in an order of how to take them, or in just a random order.   

I don't know for sure.

Post 8 grade courses, they appear to be laid out in at least a degree of logical order because calculus is last because it's harder than algebra 1 and 2 and statistics, for instance.

However linear algebra is not as hard as calculus. No where near as hard, my friend, who is gifted at math says.

Still, I'm very confident that if I completed them in the order they're given, it would work out better than if I started with pre-calculus.

Good luck in your journey.

It's incredible that this type of questions still happen. Yes, the order is the one you should follow. 
Oscar Sheen What your friend has done is not Linear Algebra probably. In the best case, what your friend has done is analytical geometry which is part of precalculus. In the worst case, he's thinking that y = mx + b (i.e. linear equations) is Linear Algebra (when is studied in an elementary course in Analysis LOL). Linear Algebra is a university level course. Knowing linear algebra helps us deal with vectorial calculus or multivariable calculus, but everything at it's time. Follow the content provided by Khan Academy jouni.santala. Why would Khan Academy want to put something not in order? It could have made sense when it started but not now that it has more than 10 years. Keep working guys. 

Thanks Pablo.

Thanks Pablo Sánchez. This gave me peace of mind.
In fact, it's easy to become unsure, not least because I have barely any math background. What really threw me off was opening All Math, and it's not in any order. Then when I looked the list I attached earlier, it starts with Algebra and ends in Algebra, so the only thing I'm sure about at that point is that I'm unsure about everything. 
Anyhow, I guess it could be clearer if I had to ask. Use a fool to see if your system is foolproof :D