all the people who are saying you have to get scouted when you're young are totally wrong.
My brother is a professional footballer so i know a thing or two about how things work. Yes, it's more difficult to get picked up or get a trial at your age but it's not impossible by any means. my brother was playing non-league football until he was 18 and then got picked up by the club he's playing at now (in league 1).
start at non-league teams.. send your football CV off to teams in the blue square. people will tell you this doesn't work, but it often does. have you played for any half decent teams, have you played county/national school-boy football?