You must be 18 to enter into a contract, they could not sign a deal for the snack shack with the town or get a business license or insurance.
A.J. says he has his own bank account, but you must 18 years of age to open a bank account on your own and he's 15.
At the end of the movie, Brooke's dad is seen wearing Air Force Master Sergeant / First Sergeant stripes. The Air Force announced changes to the stripes on Oct 1, 1991, with a long test and transition period until 1997. The movie is set in the summer of 1991, so it is a little too soon for Brooke's dad to be wearing that particular set of stripes. He should be wearing the old-style of Master Sergeant stripes known as "six down".
Brooke uses the term "cringe" in its modern slang meaning of something awkward and embarrassing, which will not become common until the late 2000s.
While taking place in 1991, the $100 bills featured in the movie weren't in circulation until 2006.
The movie takes place in 1991. Callaway did not start manufacturing golf balls until 2000.
The grocery store scene has products that feature modern packaging designs (most notably Hostess and Frito-Lay products), which were different in 1991.
At the beginning of the movie, as the two main characters run to the bus, you can see the Desert Dome in the background at the Henry Doorly Zoo. Construction on the Desert Dome did not begin until 1999.