I hope this isn't revolving around not being able to keep the school open for an extra 20 minutes so that children can eat lunch.
In my district, it appears the reasoning is based on that age segregation. They only let one grade in the lunch room at a time, and they basically lock them in for 20 minutes, so that someone else can be on the playground. It fits into a pattern, because it explains lunch, recess, and their appalling lack of support for acceleration.
Apparently, someone thought that 8yos and 7yos are volatile compounds that cannot mix.
With this as a basis, it would be impossible to extend lunch beyond 20 minutes, because then some classes would be eating too early and/or late.
