If the scene where the Flynn-Fletchers purchased Perry happened 5 years ago, then why is Carl a college intern helping Monogram, wouldn't Carl be either in Middle School or High School, and don't Middle Schoolers and High Schoolers not have internships?
https://old.reddit.com/r/phineasandferb/comments/1ue3j9h/if_the_scene_where_the_flynnfletchers_purchased/