The natural route. I say that because I started my dreads by backcombing them, and I still found a spiritual connection to it, they helped me grow as a person, understand myself, etc. And then I realised how much more amazing the journey would've been if it were completely natural. I combed a few out since then, one at a time, so I've experienced some natural journey, but for anyone whose dreads are anything more than a hairstyle, I guarantee the natural route will get you the most out of it
Simply stop brushing your hair. Wash with a residue-free shampoo (baking soda and then apple cider vinegar is good too, see more about the ratios and etc. if you want to do that) every two or three days, and separate your dreads when the sections start to join together, otherwise they'll get too big and might get pretty painful and problematic. On top of that, have patience, try not to care about how messy they can be, let it be part of one of the life lessons it teaches you, and enjoy every part of the journey, because it truly is a journey.
I'd say dread now. If your hair is too short to dread, you'll need it to grow a bit more before it starts dreading, but you might as well get yourself into the habit of not combing your hair and etc. already. But it does sound like it's long enough to dread