Weapons self defense is taught from Red belt and up. However, we teach it earlier to women, because we have a special training program for them.
You must have good self defense skills before attempting weapons defense.
The most important thing we teach our students is try to stay away from weapons on the first place, because when you have a knife on you throat or a gun pointing at your head there is very little you can do.
The key is to react fastly when you watch the attacker to seize a knife with the intention of hurt you with it (before he tries to do it).
There is no miracle technique to defend against a weapon. Maybe against a nunchaku, a staff or something like that, but against blades or fire arms there is very little chance.
Regards.