There are quite a lot of thought provoking posts on this thread, in terms of perspectives and insight to gain sunflower.
Those that say things like 'my brother was born in August and he was top of his class and is now an Oxford professor' are only thought provoking in terms of how dramatically they miss the point. These people are outliers (I'm one of them), which gives more weight to the validity of the normal distribution curve, rather than disprove or discount it.
As I mentioned earlier, people tend to regard any process or measurement as 'fair' if it favours them. Vanity or seeking evidence to confirm your pre-existing views are the main reason for this, and possibly lacking the intelligence or will to see the bigger picture.
Age cut off is a significant factor in academic attainment and self-perception as a child, which influences many factors of adult life.
It's perspectives like OPs that led to 11+ scores being aged standardised and the evidence for this view that underpins the scaled and standardised scoring of IQ tests.
And her point, that if these internationally used and recognised measures of intelligence/abililty etc use age standardisation because it is a big deal, why not organisations like PMC?
And the reason they don't is because schools want to enter the children who score highest at a particular point in time, which presents a systemic and structural disadvantage to younger children (aka the shit load of evidence that supports the summer born disadvantage hypothesis).
HTH.