I'm a little older than you
and have directed short films that screened at festivals worldwide, and due to release a feature film later this year. I've also been SAG actor for almost a decade, having worked with all kinds of directors on tv series, commercials, and feature films. Just wanted to give some context for where I'm coming from and what I've learned. In my experience having worked with and known many directors who do this for a living, here's what I know or at least what I would advise someone who is starting out interested in directing:
DIRECTORS ARE GENERALISTS WHO BEGAN AS SPECIALISTS IN ANOTHER CAPACITY
Regardless of what you're directing (commercials, television, features, shorts, etc.) -- your job as a director is to oversee a team of specialists (cast and crew), to make the major creative decisions, to be the captain of the ship so to speak. You are a leader, a manager, a mediator of all these people who are providing their creative input into the process, and your job is to filter all that into a set of decisions that in plain English can get done (lots of newbie directors or bad directors are "bad" not because of lack of talent, but the inability to steer the project to completion).
And most folks don't start off as directors. But usually as specialists in some other capacity and find their way into directing that way. And through that, they develop their own sensibility and voice based on that foundation.
For example, there are many directors who began as writers (or outside of directing -- writing is their strength). People like Woody Allen, Richard Linklater and Kevin Smith are writers. Oliver Stone is another, as is Spike Lee and Paul Haggis. Doesn't mean these folks don't develop a strong visual style, but their base or foundation is writing (and that tends to inform the kinds of projects they direct: they tend to direct projects they write). Even your very own Ingmar Bergman began as a writer, as are directors from the French New Wave (Trauffaut, Godard). In other words, if they weren't directors, they'd be screenwriters/writers.
Then you have directors whose foundation is the camera. Stanley Kubrick was a photojournalist in his early years. These folks tend to have gone to film school (Michael Mann, Ang Lee, Michael Bay, Martin Scorsese, Tim Burton, Spike Jonze, etc). It's no accident that these directors tend to work on projects that are written by others. Their foundation is technical -- and had they not become directors, they would've likely worked as cinematographers or editors -- or like Michael Bay and Spike Jonze -- directing commercials and music videos (in their early career). This is probably the most common route for most aspiring directors: go to film school, graduate and work as a cinematographer, editor, etc. and work your way up, directing commercials, music videos, corporate videos, etc. David Fincher didn't go to film school, but who began his career working at Industrial Light & Magic as a camera operator. It's not accident that these kinds of directors as a group tend to have a very strong visual style.
Finally you have directors that came in through acting. Folks like Ron Howard, Clint Eastwood, Ben Affleck, Kenneth Branagh, Jon Favreau, Robert Redford, Penny Marshall, Mel Gibson, Woody Allen (as a stand up comic and writer), and so forth. It's no accident that these directors tend to get consistently strong performances from their actors (and the kinds of directors that A-list actors LOVE working for).
As you can see there's no one way to get into directing, but most tend to find their way into directing by plying their specialist trade in some other related discipline. Of course directors can love all three (writing, camera, acting), but most of us tend to gravitate towards one more than the other. That will help dictate your path - again most aspiring directors tend to go the technical route (film school, or working on set behind the camera as a crew member/technician/camera op). It will also in a way dictate how your directing career evolves.
Personally I didn't intend to direct at all, and came through as an actor. But if I knew at the age of 16 that I wanted to direct, I would've focused on going to film school, or art school.
So that is what I suggest for you. Do the following:
1. Enroll in an acting class. A lot of directors who have no acting experience are TERRIFIED of actors or have a hard time figuring out how to direct them, how to push them in the right way. Learning first hand what it's like to be an actor will help, learning the language and different approaches/methods actors use will all help.
2. Take art classes. Filmmakers have been ripping off the great artists all along when it comes to lighting (Caravaggio, Rembrandt, Vermeer, etc has been cited as big influences for example in terms of lighting and composition). Getting a sense of color palette and composition in the purest sense - without the distraction of technology, different cameras, etc. It's about learning visual sense. Also, early on it helps to learn how to draw -- which helps if you're storyboarding your own stuff when you are making your first films (or even trying to tell the story visually). Visit museums and art galleries regularly -- it helps you develop your tastes (colors, textures, composition, etc) -- all of that will help you as a director - not just for camera, but in figuring out an overall style for the film which helps wardrobe, production design, location scouting and so forth.
As an aside: too many folks get obsessed with camera technology and confuse that with "filmmaking" at least from a director's perspective. These folks have such strong opinions about RED vs Alexa, Avid vs. Final Cut, etc, but ask them to discuss fashion/clothing, architecture, furniture and colors -- and there's almost no discussion (or they're completely ignorant).
3. Read a LOT. Become familiar with great works of literature - plays, novels, memoirs, etc. And watch a LOT of films - both the great and awful. You don't need to go to London for this. This will help you develop a strong instinct for storytelling. You don't even need to analyze why something works or not - just by sheer volume, it'll be an instinct, and should you write your own screenplays and/or in the editing room -- you have a strong gut feel for what works and what doesn't.
4. Focus on the above 3, and avoid getting obsessed with technology. Too many folks I see become bogged down worrying about gear rather than the above which is forever and doesn't change (storytelling, performance, and visual sensibility). Yes it's fun to talk about the latest camera, lenses, shooting in higher resolution formats, etc - but when that is all you talk about or that is what you mostly talk about, you are not an artist - you are a technician.
Most great filmmakers, writers, actors, etc. don't always make great teachers, because they may not be able to explain WHY something works or not (or why they made a certain choice) - they just have developed a strong instinct through a lifetime of work to know what works and what doesn't.
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