Regardless of age, "ore" is a term that males are expected to use only among friends. It's not very polite to use it when speaking to someone older than you or someone you don't know well.
The nuetral term for a 14 year old male to use is "boku". This term can be used at any situation if you're as young as 14. But then, it's not really too weird for a 14 year old boy to use "watashi" either.
When you become old enough to teach, however, you are expected to use the term "watashi" to your students and colleagues. Let's say you are a 22 year old man. You should call yourself "watashi" unless you become good friends with the person you are talking to.
Gender identity disorder (GID) is commonly known in Japan as "sei-dou-itsu-sei-shougai". Some people may not like the "disorder" part of the term, but I'm afraid that's how it is known today. There is great awareness in schools for low-teens, be it successful or not.
As far as approaching penpals are concerned, I think there are two major ways.
1. Post an ad saying you are GID, and only accept those who approach you.
2. Get to know your penpal first, and when you feel that you have known each other, bring the subject up casually and see how it goes."私は男性でもない、女性でもないけど、女性の体で生まれました。代名詞的には男性で呼ばれてます。" My Japanese friend given me this sentences for examples. Does it sound strange?
Well, it doesn't sound strange to me, but you can make it a lot more simple:
"I was born as a female, but I think of my self as a male."
Lastly, maybe you already know about Akira, Root and all these androgynous culture in Japan that NHK has been happy to introduce to the world.http://www.nhk.or.jp/kawaii-i/archive/archive_140112.html