My DS is June-born. He's big for his age and pretty bright, but I still think age just four is far too early to start full-time education.
Another poster said that legally, in England and Wales, children don't have to go to school at all, and particularly not full-time, until they are five. We tried to arrange this with our lovely, open-minded village school and were told that DS would have to attend to some degree when he's four, otherwise we'd likely not get a place a year later.
However, if you are genuinely concerned about this early start, you can legally treat Reception year as an extension of pre-school, and have your child attend part-time (to secure their place) until the term after their fifth birthday - irrespective of the school's "policy".
I don't wish to single my son out in this way, but because eight out of the 15 children starting school with my DS are summer-born boys, three mums (including me) are considering extending the part-time phase for up to a year, so DS wouldn't be an oddity.
There is considerable evidence to suggest that age four in and of itself, let alone a young four, is too young a school starting age for most children. Where our government needs to be taking on board this research and looking to better-performing countries whose children start full-time school between ages five and seven, instead it's moving towards getting pre-schoolers to learn all their phonetic sounds and write their names pre-Reception. Barmy, IMHO.
I realise the OP's situation concerns secondary entry level, so this isn't much help. Sorry. Not altogether irrelevant to other posters though.