Late tweens/young adults 10-15 are level 1-2.
Young Adult/adults 16-26 are level 3-5.
middle age adults 27-45 are middle age, levels 6-12.
The silver years are 46-65, levels 13-15.
Elder is 66+ and is level 16-20.
Standard NPC's will never access magic over level 20. Their magical exposure is typically prosaic and training package magic, though guilds often guard those with an intense jealousy.
Using EV and OCC, a single spell list can easily reach level 20+ by middle age, so the higher level prosaic spells are not rare, yet remain just out of everyday on availability. Waiting list, contacts, good reputations and bribes are common routes players ply the game with to gain such worthy audience.
Also, most skills are developed one ranks per level. With only 50 dev, NPC's cant afford a bunch of 4/12 cost. Insteasthey excel in their skill set relying on the EV ratings all Laymen apply to the skills of their hosen/born into profession.