He was probably about nineteen or twenty when he created it, and it's part of what earned him the El-Melloi title; as a result, it's connected to the title rather than his actual crest, which is why Waver managed to inherit it after becoming Lord El-Melloi II. I think he intended to create something that could passively serve as both the perfect defense and offense just because, so it's really a little of column A and column B. He was also pretty into dueling other students at the time so he did it purely to see how effective it would be, but it ended up working so well that he ended up even more bored than before he started...