What you say sounds fair but it's not what the section on standardisation on this site suggests.
See http://www.elevenplusexams.co.uk/standa ... scores.php
This indicates that older children require a higher raw score than their younger classmates. I'm happy to be wrong, it's not something I have looked into as it doesn't apply to my region.
I have no axe to grind on this issue. I just never found age to be a useful indicator of ability within a class of children - even in reception where some (unfairly, in my view) had only one term to their older classmates' three. If I had a child who was at the younger/older end of the intake and lived in an area where this was deemed relevant, then I may take a view tainted by my own situation. As it is, I don't.
What happens to children born two months prematurely? Are they judged against those with the same birthday but who were at full term or against those of the same developmental age? Some children born early will find that they are in a different year group than they would have otherwise been. I just think a line has to be drawn somewhere and that a year group should be treated as a whole.
Sorry for digressing.