You may want to create a group for each age category within an event. Create an automation to add attendees from a Registrations event to a group.
The following steps require permissions in People, Groups, and Registrations. This process can be a collaborative effort with people who have those permissions, or an Administrator in those applications can give those permissions.
Create a List
Once you've created your event, create a list in People for the attendees who have registered for the event. Make sure to add the specific Attendee Types or other criteria for the people that you want to add to the group.
Make sure you set the event to auto-refresh in the Settings, which refreshes the list every day.
You can set a list automation to add them to the group, so as people begin the register for the event, they are added to this list, which then adds them to the group.
If you don't need to attendees to automatically be added to the group, you can use bulk actions to take the same step manually.