It definitely is possible. I think the fastest progress that I’ve seen yet was @lopicake who basically did it in less than a year.
However, as others have said, better don’t try to compare your progress speed to others’. Considering that you’ve created a thread “I’m not renewing WaniKani” just a few hours before this one, it seems that you are unsure if you even want to do WaniKani in one go or take several breaks. I personally think the lifetime subscription would be the best in this case (there should be starting a sale next week which most likely reduces the cost of lifetime to 199$).