Matthew, it's great that you're so young and getting into pre-war baseball cards. If you have friends in the hobby, you might encourage them to check them out, too. Vintage and pre-war cards are a lot of fun to collect.
I will give you the same advice I'd give to anybody first starting out. You want to start out figuring out what you like. You've done that to an extent by narrowing it down to T205 and T206 cards.
Before you start buying your cards, there are a few things every collector should have.
1. You need a magnifying glass or a jeweler's loupe. There are ones made with a light source. That's nice to have if you're at a show where the light quality may vary. But you want something with at least 10 x magnification.
2. You want a black light. Why? A lot of alterations will show up under black light. If somebody has used a marker to make a black edge look better (example 1971 Topps cards), you'll see that with the black light in a dark room. If somebody has repaired a card, ie added paper to the card where there was paper loss, that will show, too. Between the loupe and the black light you're going to be able to see the vast majority of alterations that might be made to a card.
3. You also want a ruler to measure cards. One thing to keep in mind with pre-war and even vintage cards-there may be a little variance in the size of a card. And that doesn't necessarily mean that a card has been altered. It's good to give you a baseline.
Here are a couple great guides you want to read, written by David Cycleback, who is a member of our forum. I'm going to link articles that talk about
uv and black light.
Next, here's something you want to read, also by David Cycleback. It's a book about
Judging the Authenticity of Early Baseball Cards. I bought this book on Amazon, though David makes it available on his website. I like having the option to take the book with me wherever I go. That's something I strongly recommend reading.
The other thing I highly recommend having is a common card for whatever set you plan on collecting. If you decide that you want to start collecting the T206 set, make sure to get a common T206 from a trustworthy source (the members of this forum are a great bet. Also, there are many trustworthy dealers, names that you will get used to using as you build your collection. Anyway, once you get that base T206 card, take out your loupe/magnifying glass and your black light. Look that card over, first in ambient light, then under black light (in the darkest room possible). Look at the edges of the card, feel the paper stock, look at the printing. You need to learn how T206 cards were printed. Once you understand that, you'll begin to look for the black border of the T206 card, and see where you might have a color bleed outside of the border. If the card has any heavy fraying, look at the card stock. You might even take a single-edge razor blade, and cut along the edge. Why? Because one of the things you have to be on the lookout for as a pre-war collector is trimming. Unscrupulous people will take a single-edge razor to a card with rounded corners, and trim some of the side off to give the card a cleaner edge, and sharper corners. By slicing your card on one edge, you can compare what a factory cut edge looks like under magnification, and then what a trimmed edge looks like. If you see a T206 card with uneven corner wear, there may have been some trimming.
The most important thing you can do as a pre-war collector is to handle the cards you want to collect. Look at them any chance you get. If there's a vintage or pre-war card show happening in your area, or if there's a card dealer that sells vintage, go and look at the cards. I'm not kidding when I say that I pulled my first ungraded card out, and smelled it, felt it between my fingers. The more you look at these cards up close, the safer you will be. Once you've handled these cards for a while, and you feel comfortable with the set, then you can start looking at some of the more expensive cards. And when you buy those, take scans/pictures of them, and have the members of our forum look at them for you if you have questions.
Maintain a healthy skepticism. Always keep your eyes open. Trust your instincts. If something looks off, or feels off, ask us to help you out. Buy from forum members and trusted dealers. By doing these things, you greatly reduce the likelihood that you're going to be taken advantage of.
Most of all, have fun!