Are you in the UK, Cleo-pattie ? (I think you must be, because you wrote "theatre" and not "theater" !) If so, then take a look at what Rose Bruford College has to offer. (Rose Bruford - one of the Conference of Drama Schools that gives automatic Equity membership etc.) They run a B.A. degree purely in Directing (whereas a lot of the drama schools only run a post-grad one year directing course - e.g. RADA). Details of the course here: Rose Bruford - BA (Hons) Directing
Rose Bruford run regular open days for prospective students and I'm sure that if you contacted them, they would be happy to give you advice. As you will see, theirs is a 3 year course in directing, culminating in a London Showcase.

It seems to me that you are giving yourself a lot of good all-round practical stage/tech experience in school AND outside school, which, as others have said, is the best preparation. Have you enquired at your local regional theatre ? As well as needing volunteers for all kinds of tasks, a lot of them have "studio spaces" or foyers which they hire out at a very low rate for one-off showcases on Sunday evenings, for example. I know for a fact that the Queen's Theatre, Hornchurch (London Borough of Havering) does this - and I'm sure other regional theatres do this too, to encourage local writers/performers/directors. That would be great experience for you to get a group of friends together for a one-off. Then...for bigger adventure... the Edinburgh Fringe ?

Another place to contact: the National Youth Theatre (www.nyt.org.uk) which has a technical as well as an acting section.

(Forgive me if you know any of this already !)

All good wishes. Let us know how things go.

- jeanie