Age ranges are based on the standard Pathfinder age categories for a human, combined with some historical British education practices - and are used as a base for all ‘ordinary’ NPCs. However, race, temperament, etc., may mean that some children (normally PCs or ‘special’ NPCs) finish earlier or later.
Sometimes known as Infancy, young children rarely have any real responsibilities. In the countryside, they might play in the fields as their parents and siblings work alongside. In a town there might be a stay at home carer (such as a mother or grandmother), or a child might accompany their parent, or an elder sibling might be left in charge.
Life gets more serious at about 7 years of age. Older children are expected to start preparing for adult life and start taking responsibility. It isn’t unusual to see 8 or 9 year olds running errands and delivering messages without supervision. Just about everyone growing up get a basic education of some sort – and learn basic literacy and numeracy skills. When they get to 15 years old, characters become ‘adults’ as a L1 Commoner . Some lucky ones go on to train as more prestigious classes.
A few lucky students get to continue their training, although most go on to start their adult life as L1 commoners. Some students go back to work in their family business. Others find a mentor who will teach skills in exchange for menial service, while others can find the money to pay for extra schooling at a college or an academy. Use the standard Starting Age rules to work out how long training takes for characters to retrain into a PC class. For an NPC Class it takes about half the indicated time.
Most Craftsmen and Professionals are self-employed or manage a business for an absent ‘investor/employer’ – and are able to control who they employ and what apprenticeships are offered. In most cases children ‘apprentice’ within their own family and learn family skills directly from their parents, and carry on a family tradition. Sometimes, however, children might train with a family friend, or ‘swaps’ arranged. This works really well for Experts going back to the family business or even Aristocrats getting brought up at home. This type of training arrangement could last years, and the ‘apprentice’ might stay in the business, gaining levels slowly, until they take over from their parent!
In a traditional apprenticeship, a character goes away and study with a ‘master’ who teaches skills in exchange for menial work. Sometimes these arrangements go on for years, with the apprentice eventually becoming an ‘Assistant’ - although they still learn and progress. A 'traditional' Apprenticeship lasted for seven years, although some (such as an Arcane Magic apprenticeship) might last for much longer.
The Torchbearer, Squire, Imperial Knight and Recruits feat provides advanced apprenticeships that can train the apprentice beyond L1 quite quickly.
If they can find the money, students can continue their formal by attending a Finishing School. Many Finishing Schools have links with Day Schools and Private Schools and there can be a fairly smooth passage between the two for children from wealthier families. However, these schools are businesses and most offer part time courses so that they can attract students who need to work to finance their education, which means the time students have to study to achieve their new class varies. If you use my Campaign Rules
Academies, and Universities provide the same sort of training - but to a higher level and (sometimes) in more prestigious subjects.