It might help if we had a sense of your budget. Are you on a tight budget like many 16 year olds, or can you afford to buy nicer blanks and pen kits?
Here is my advice:
* Turn wood first. Wood is easier and more forgiving. It won't take long before you are good at it.
* As soon as you have roughed your blank from a block into a cylinder, you get a chance to practice and play. If you make a mistake, there is plenty of wood left to fix it. Here are some things you can practice and play with:
Try different turning tools to see how they work and what they can do.
Compare high speed steel (HSS) versus carbide turning tools.
Learn to make different shapes - beads, coves, V's, lines, etc.
Practice with a skew chisel until you are so good with it that sanding is unnecessary.
Try burning with a wire.
Learn how to turn a perfect cylinder pen. Check your work with calipers and a short straightedge with a white card behind it.
Finish the pen with CA. Turn it off. Finish it again with CA. Turn it off. Repeat until you are good with CA finishes.
Try other finishes. Finish, turn, repeat.
-> Once you reach a certain point, you should stop practicing and focus on turning the pen-in-progress.
* Buy spare tubes to match your pen kits. Spare tubes remove the stress of worrying about turning failures. If something goes wrong, just grab another tube and some wood, and don't look back.
* Wood for pens is easy to find. You can cut up almost anything wood to make pen blanks. Dry wood boards can be cut into pen blanks. I have also made pen blanks from old furniture and fallen branches (after drying). Put out the word and you will get plenty of wood. Ask your parents' to ask their friends. Talk with teachers, social groups (like church families), etc. Scrounge around shops that work with wood, like cabinet makers. Very quickly you will find that you have a great deal of wood, much more than you can use. Most of it will be plain and uninteresting, but It will make nice wood pens that finish well and feel good. Soon you will learn to seek out the better woods that yield better looking pens.
* Find a woodworking club in your area. They may be able to offer advice and experience, plus maybe spare tools or wood.