By the time of the 13th century, there was a fairly strict process to becoming a knight that became uniform throughout the Medieval world, pioneered by the practices and traditions of England’s noble class. Young boys from well-to-do families would be sent off at age 11 or so to the houses of other nobles, where they would become pages, effectively boy servants tasked with carrying out menial errands and such while being taught in the skills of writing, reading and swordplay.
Around the age of 14 they would eventually be granted the title of Squire and tasked with shadowing a superior Knight, looking after his armour and cooking meals for him etc. Squires also saw real combat fairly often, and this was seen as the true test of their valour and if they had earned their knighthood or not – many squires died a gruesome death on the battlefield. For those that survived however, after years of service, during his late teens or early twenties a successful squire would finally be given his knighthood. This could theoretically be granted by any knight, but the ceremony was often conducted by the local reigning lord.