Just wondering what the most improvement in each category anyone has seen is (from a non-ditr)

Up to low 30s. 

I typically draft 18 year olds so I don't have as much experience with college guys, but my rule of thumb is that for an 18 year old to not expect a guy to improve 35 points in any category (I can't remember that ever happening for one of my blue chip prospects) no matter what the projections may say.  30 will happen sometimes but 35 would be vary rare.   

I would expect with college guys the highest improvement range to be less, especially in the physical trait categories.  

I'm not sure ive noticed more than 18 or so in v.L and v.R from the start of first complete season. Is that low? Am I likely missing something or failing to fully develop guys?

Actually some low 20s in those categories

Well development starts from when they are drafted.  In a guy that is going to get 30+ you will normally see at least 4 or 5 point in the first season in the learned skills (like vR and vL) and more than that in the physical skills.  I have had guys increase by 10 OVR from draft to the first season mark.  So the first full season you see on there card they will have a good amount of development already.  Again these are 18 year olds who have a good amount of physical projection left.  

My best prospects I will make a note of their starting ratings to see how they do when fully developed.