I get why everyone is posting feelgood messages here, but again, unless I gravely misunderstood OP, that’s not what he asked.
He didn’t ask “what rank should you reach before starting a club” (a topic I’ve actually addressed in another thread) “what rank should you be before promoting the game” or “what rank should you be before passing on someone else’s teachings”.
His question is quite literally
What level should one reach, before… [giving] reviews and [playing] teaching games.
Now I’ve seen some 20k+ - 20k+ “teaching games” and it was nonsensical variations upon nonsensical variations. That’s why I’m saying variations only make sense if you know what you’re doing. If you’re not at least at the cusp of reaching SDK, your strategic ideas (i.e. anything beyond reciting proverbs) are probably not going to be very useful, either. However, if you’ve got at least 9 stones on your opponent, merely by virtue of playing someone stronger, they will be able to benefit from the game.
However, I do think there’s some distinct advantage to everyone discussing their intentions for any given move or sequence, as it might help develop strategic thinking.