My DS applied late as wanted to move from his vocational school to one with boys only ballet classes (he wanted a classical focus). We applied after Easter when he was in year 7 and managed to get an MDS for Sept Yr8. A girl auditioned at the same time and was similarly successful (from a diffferent original school). If they think your child may have potential, most schools will always consider them, if for some 'good' reason you missed the initial audition dates and have NOT applied before for previous years. We avoided the nightmare wait that way! He auditioned and was told of the outcome on the same day.
Never underestimate the rollercoaster ride though. My DS now does not dance at all, he never regrets his decision to start or then to stop, but he decided after a few years the life was not for him. Remember your child may change their mind, despite being ballet mad for years. A shock at the time, but he made the right, and a brave choice - I know that now!
Always worth a try is my motto - whatever you want to do.
Good luck to you all.
Fx