We don't know what sort of development you're doing or diagrams you're talking about.
If they're design diagrams, why are you printing them? Spreading a diagram across "pages" is painful when you're trying to read online and have essentially infinite zoom capabilities. If he wants to do single-page diagrams in four-point font, click that little "+" or drag the slider and zoom in on the part you want to see.
Unless his code doesn't work, or someone assigned you the task of cleaning his code up, I'm not sure why you're complaining. Guess what - real world code, especially internal code, sucks.
I work on a C/Unix code base that dates back to 1986 - a time of 80286 processors and Xenix. It's grotesque. There are globals everywhere to deal with lack of stack space, it's K&R, and each programmer had their own idea of "correct" tab stops, so the first thing you do is play with that until things look like they line up in the function you're working in. It might be different elsewhere in the file.
There's code that hasn't been executed (we hope) since the early 90's, but we leave it unmolested until we're actually changing that file for other reasons. Then, and only then, do we consider carefully excising it - because if you change it, QA has to test it before it's deployed to roughly 15,000 systems scattered around the globe with poor network connectivity back to the main office.
Maybe you're not cut out for maintenance programming and dealing with someone else's code base. Most people fresh from school aren't very good at it and want to "fix" everything. I suspect that's who you are.