How long does a black belt take?
It is the first question almost everybody has and the last one that turns out to matter.
The honest answer is four to six years of training two or three times a week, and the reason for the range is attendance rather than ability.
A first-degree black belt in Shotokan karate usually takes four to six years of steady training, at two or three classes a week. What decides it is attendance rather than talent: the belt marks the hours put in and the standard reached, and there is no version of it that arrives faster because somebody is naturally athletic.
Why it takes that long
A black belt is not a syllabus that can be finished quickly by somebody clever. It is a set of movements that have to become automatic, and automatic takes repetitions that cannot be compressed into a shorter period by trying harder.
Grading happens through the coloured belts along the way, each one with its own material, and each one is a checkpoint rather than a reward for time served.
What actually slows people down
Missing classes. A person training twice a week gets there. A person training twice a month is doing something worthwhile but should not expect the same timeline, and being told otherwise would not be a kindness.
The other one is stopping and restarting. Two years off does not reset everything, but it does mean a period of getting back what was there before, and that time counts.
What a black belt actually means
In Shotokan it is first degree, shodan. The usual translation is not "expert". It is closer to "the basics are reliable enough now to start learning properly", which is a smaller claim than the belt looks like from outside, and a truer one.
Most people who reach it say the same thing: the belt mattered enormously right up until they got it, and then it turned out the interesting part was everything after.
For a child
Children usually take longer, and clubs are right to make them. A junior black belt awarded at nine because a child has been attending for four years serves nobody.
The better question for a child is whether they are still enjoying it in year two, because the ones who are will get there, and the ones who are not were never going to.