In Malcolm Gladwell’s worth-reading Outliers, he makes the case that developing expertise in anything requires 10,000 hours. It’s a rule; the ten-thousand hour rule. If you work 2,000 hours in a year, that means it takes five years to become an expert.
There are lots of examples of this in practice; to me, it seems roughly right.
For example, in late medieval Europe, this rule seems to apply to the guild craftsman system, vestiges of which still remain. You apprenticed to a master for a period of time, typically three to five years, living with him like a son and learning the trade. You might start out sweeping the floors and taking care of the tools, but you progressed to working alongside the master or, if he had a large workshop, journeyman craftsmen, but always under the supervision of the master. After your apprenticeship you were sent out into the world as a journeyman yourself, with your reputation at least initially dependent on the reflected prestige of your master.
This guru-disciple relationship was formally regulated by the craft guild that the master belonged to; only masters could have apprentices and only masters belonged to the guild. In order to get master status you have to submit a ‘masterpiece’ to the guild.
[Edit: See also Ira Glass on spanning the gap between taste and ability.]