We've usually seen equal age divisions named either boring old names (child, junior, senior, etc) or special names for a themed meet (snowflakes, etc). The exception is states, where they go by age number and split within that age number. So there may be ages that don't get split that have less or more kids than the subdivisions of groups that do get split, if that makes sense. So maybe there are 20 7 year olds in one group, but 30 8 year olds who get divided into 8A and 8B so they are smaller groups of 15.