What I would give to be sixteen again and have the collection that I have...Sheesh!
First thing is to relax. Breathe in, breathe out. You're sixteen. You should be thinking about dating and homework and college and getting a driver's license. Don't be so worried about building skills you have (or don't have). Doing well in school should be your first task. School will teach you how to learn, how to analize the building techniques of the great MOCs we all love to look at. Taking some drafting or wood/metal shop classes would help.
As far as your MOCs you have some decent stuff there. If you think that you need something more dynamic designs search the internet(if available) or the library for books on Castles or other fantasy structures. Then plan your build in steps by drawing them out on paper. If you try to build everything at once you'll get frustrated and stop. Think about your MOC like a text book - Chapter one is the Drawbridge, Chapter two is the surrounding towers, etc, etc.
At the very least you have joined the best site on the net for learning/discussing LEGO Castle. Welcome and enjoy.
Power corrupts, and absolute power corrupts absolutely!
Despise learning and make everyone pay for your ignorance.
The water that floats a ship is the same that sinks it.
My LEGO figures keep me from being evil, drat!!