Bsrgvty

I am currently 15, live in a small town in Switzerland and have a green belt. There is a small, local Judo community that mostly trains young children from white to orange belt. There are currently three masters that lead all groups. I do not plan to become a great fight winner, my plans are more about being someone who helps young people at the very beginning of their path.

How far do I need to proceed within the rank system before being allowed to train others? Apart from simply training and moving ahead with the belt color, should I do something more to fulfill my plans?

Generally the way to become a good instructor is experience.

Instruct at your club whenever you have the opportunity - get better at dealing with students and explaining things in a way that they understand - watch your instructor teach, how do they make it simpler for those that are struggling etc. (or maybe - how would you explain/demonstrate it differently if you can see people struggling)

Attend everything - not only will this help your ability/technique - but your eyes will be opened to the different worlds of Judo out there. You don't need to win tournaments to know "how" to win, but if your future students are interested in competition, how do you lead them confidently if you didn't enter them yourself?

Seminars with high ranking instructors are also a great way of improving your technique as well as picking up new ways of teaching old moves. (Almost none of my teaching is my original creation - it's all stuff I have picked up from my instructors and seminars I have attended)

Also Talk to your instructor about your desire to be an instructor, there is no shortage of martial arts instructors - but there is a huge shortage of good martial arts instructors - who teach good applicable technique and want the best for their students. Your instructor will likely be thrilled with your desire to teach and will guide you down the correct channels for your particular art/association. (there may be age restrictions on you becoming an official instructor - but i'd still advise helping out as much as possible and getting prepared for the day you are old enough)

What rank to help teach?

There is no minimum rank. The head instructor must have confidence in your abilities and have a need for assistance. In smaller clubs, you may be one of the most advanced students as a sankyu, and the instructor may request that you sometimes assist instructing junior students. At large clubs, this may be the role of a higher rank such as a nidan. You will probably be asked to help with basic skills like falling before more difficult skills.

Breadth

As a competitor, you can specialize in a handful of techniques suited to your own body and affinities and then mostly ignore other techniques. As a teacher, you must have sufficient breadth that your students can find their own specializations from your instruction. It's not sufficient to have one amazing tokui waza (favorite technique) because your students may not be able to reproduce the same technique with their bodies.

Organization

It's not sufficient to be able to teach techniques; you must organize them in a coherent way for students. For example:

• Drop seoi nage is not a good first technique to teach because it is not suited to building combinations. Although a competitor can learn it first and go win competitions, it may restrict their future development.


• 
  Harai goshi is harder than tsurikomi goshi. If you cannot throw a hip throw standing on two feet, than throwing while standing on one foot will be harder.

Clear ideas

As a student, think about what makes judo hard to learn. For me, this includes:

• conflicting instruction about how to perform nominally the same thing


• rote memorization of directions without understanding why


• hazy instructions

Fix these things in your own instruction. If this means you need to do more independent study or consult other teachers or resources, do it before you pass confusion on to your students.

Resources

There is a decent book The Teaching of Judo by Mark Roosa that I recommend because it is precisely about teaching, not competition.

There are really two skill sets you need. First, is a good understanding (both physical and theoretical) of Judo. Second, is a good understand of teaching physical activities.

For Judo specific knowledge, getting through the grades and doing some competition is essential. After all, first dan is knowing the basics; second dan is being able to do the basics; third dan is understanding the basics; and fourth dan is being able to teach the basics. However, you should be able to assist teaching at first/second dan and do your own classes at third/fourth. Of course, nothing whatsoever stops you from teaching earlier. Most organisation can certainly train assistant and full instructors at whatever rank they chose to. I have seen great teachers that were shodan and garbage ones that were rokudan.

Going competitions is essential as it will not only improve your understanding of kata but will give you experience of using your skills against resisting opponents. This is essential in understanding how to apply kata. Clearly, you should be able to perform the techniques adequately for your grade, although being a competition winner is not required provided that you did do some competition.

Teaching physical activities is a vast topic. There are whole university courses for this and while they are useful unless you wanted to become a physical activities coach professionally you do not need that level of details. However, you need to know how to coach people and I am sure Switzerland's Judo association will be running course for that. I would check those out in the first place.

In addition, you will need a first aid certificate. You should get one anyway. Everyone should get one. 'nuff said.

If you teach children (aka under 18), there are a myriad of regulations you need to follow. Again, your parent organisation should know all that. The law is quiet complex in that respect. You can get into a heap of trouble there without even realising you are.

Finally, since you are 15, I would strongly recommend learning and practising as much as you can. In ten years, you will be a third dan and in a perfect position to start your own club. In the mean time, ask your instructors what you can do to help. I am sure they will appreciate the help!

I would argue, "wait and move to a bigger city". A small town doesn't have enough kids to sustain a good club of any sport, unless there's a particular interest in that sport.

Moving between countries and clubs over several decades, I've seen many clubs. In 500K+ cities you may find 5--10 adult clubs with two clubs training at the same time, one competition-oriented one more recreational; the same club can have a technique-oriented training one set day and another more fitness and randori-oriented. My favourite club had a good level recreational training (7th dan sensei, 4th dan assistent and several more temporary 2--4th dan, mostly university students) with a specific classes for autistic children and a strong social focus (hah, so many house moves followed by beer!). Your club needs a good mix of fresh blood and experienced older people, bulky strong and wiry fast, overenergetic bears and deliberate pythons.

Teaching kids 3--6 is VERY different from teaching young adults 18--25. For one, they're differently motivated (parents sent them vs. self-entered; though both may be hanging with mates more than learning), different attention spans, and in the adult group there will be many skilled ones showing beginners how it's done while with the kids they're essentially all beginners.

I have always the feeling when you're a teenager that you want 2 trainings/week to stay at the same level, 3 to progress.

I completely agree with what collett89 replied.

And since I don't have the ability to comment an answer I'll write this one to add two little things since you are in Switzerland:

This one kind of certification you can get to teach
https://www.jugendundsport.ch/de/sportarten/judo-uebersicht.html

This is the agenda of the Swiss federation, check the seminars
https://sjv.ch/agenda