How old was Kurt supposed to be anyway? I mean, I find it a little broad to believe that someone who is seemingly a teenager (or, at least, very early 20s) is the owner and founder of a humongous burger joint that was also supposedly going to expand into a chain of its own. Yeah, I know it's a kids movie, and not entirely impossible (apparently, there's a 14-year-old girl in Florida who is quite a real estate tycoon), but still...
He could have been intended to be in his late 20's or early 30's; even 15 years after the film you can find college-age "young adults" and graduate students that have the same style and personality as Kurt (mostly in Business-based fields). Further, he has a distinctive edge over his competitors: it seems like he's giving more burger for the same cost. And all this is before considering the connections he has in order to have initially acquired his illegal chemical additive; he could have been well-off before he started his business.
What exactly was Ed's sauce again in Real Life? I seem to recall reading or hearing that all it really was was a mixture of ketchup, mustard, and mayo in the right ratio to give it that bright orange color, but I don't remember that coming from a confirmed source. It would make sense though. Oh, and let's be honest: the sauce was pretty much orange because this was a Nickelodeon movie, wasn't it?
How did Dexter not already know that Mondo Burger used illegal chemicals to enlarge their burgers? Yes, he only worked there for a short time, but you could clearly see the triampathol boxes and cans on the shelves.
He didn't work in the kitchen, and I guess only Kurt's most intimate employees know it.
How was Mondo Burger able to charge the same prices as Good Burger? Using a black market chemical to enlarge their burgers would probably end up costing them more than simply using more beef.