I am an artist that makes a living writing music. I primarily do sound design for movie trailers and the occasional chinese x-box commercial. I'm 34, and even with a degree in 'electro-acoustic music composition' from a state university, it hasn't been easy. You don't need to be a member of the screen actors guild, ASCAP, or BMI. you DO need to be a member of a performing rights society (ASCAP,BMI,PRS in the uk i think?) if you want royalties for placements you've received in the past.
you need to be able to create any work asked of you on demand. I can't tell you how many times i've gotten a brief for something (like a TV network rebranding and needing a new sound ident. HUGE stuff) and had less than 24 hours to submit as many pieces as possible. to create on demand you have to get past the common misconception that one needs to be 'inspired' to create. Art is a blue-collar job and you show up every day to put in your time, whether you make a masterpiece or absolutely nothing.
W. Somerset Maugham was once asked if he only writes when inspiration hits. his reply "Of course I only write when i'm inspired. Luckily for me, inspiration hits me every morning at 9am sharp!" When you treat it as a job, it will become one.
Make music every day. The more you write/produce/record/design, the better you get. I've had many friends and a few fans (as a dj, played a bit in the states) say i'm 'really talented'. I'm my own worst critic. I can think of maybe two tracks i've written over the past two years that i can listen to and actually dig. Talent is nothing more than a natural proclivity towards a specific discipline.
Granted, this has been my experience. I love the creative process, and I love spending days crafting some strange lead or sound for a track, but the consumer (as in those that will 'consume' your work) doesn't care about the process, only the product. work hard, work a lot, and work fast. some of my biggest successes came from that third tune i wrote in one day, or that last idea i sketched out after a day of writing complete filth.
also, my wife works in the industry, she's had a few different positions in the past, but artist development is her real passion. Our relationship has never aided me in the industry—it often makes things trickier—but I know she's been working with my music supervisor friend, and wants to start scouting talent here for placements in the states. I work exclusively with them, and i'm sure my wife will be interested in any artists here with content for placements.
pardon me for the long post! and pm me anytime if you wanna talk. I have to get back to work on a remix now.. on spec!