According to this YouTube video, creator Chris Savino has stated that he never wanted the characters to age up and he never wanted Lori to move to college.

https://www.youtube.com/watch?v=j_zu4opE1tU

Here's the transcript (starting from 11:26):

"Personally, I don’t like to see cartoon characters age. So I don’t like that they aged up into different ages as well as grades in school. It was always a thing like never have a birthday for a character because then you have to tell...well, they well knew the ages but it was like, of course, if they’re now 12, well doesn’t that mean they have to go to a new school or aren’t they getting older school-wise, like it just caused a lot of problems more than solutions. So...just to backtrack a little bit, I just don’t think that they should have gotten older. I don’t think Lori should have gone off to college."

If he saw this petition and this DeviantART group (https://www.deviantart.com/donotageupthelouds then he'd be happy to know that he's not alone in his statement.

Thank you, Christian Car Rides, for providing us with this information."