I'm quite familiar with making custom careers for adults, and there's tutorials on how to do so along with tutorials on making majors, but I have yet to find a tutorial on how to make custom careers for teens. Can I just download another teen career, scrap all the text and icons and such so that it becomes a blank "template," and just use that? Or are there actually any tutorials? I've searched, trust me.
I am a Slytherclaw! And totally the obvious demigoddess daughter of Aphrodite, pssh heck ya.
I have no idea how I learned to make teen careers. I'd suggest using a downloaded one as a base. If you're not comfortable using a random creator's career as a base, in case it bothers them for some reason, feel free to use my teen Falconry one :-) I think that I used one of the Maxis ones as a base for mine, but I'm not 100% sure.
I can't recall ever seeing a specific tutorial for them, but I'll keep an eye out and let you know if I come across one :-)