According to Mitchell's parents, he will be spending 6 months in Ohio. In the restaurant, when Jack tells Mitchell that "he's driving Nikki home", Mitchell responds by saying he's been there for 3 weeks, and in the next sentence tells Jack that he's leaving in 3 months. 3 month + 3 weeks = (not 6 months)
During the skate scene, the beginning of the race shows them coming down Springdale Road - which is in Ohio, about 10 miles from Cincinnati. A few scenes later during the same race, the skaters are coming down Devou Park hill - which is in Northern Kentucky. The entire race scene bounces back and forth between Cincinnati, suburbs and northern Kentucky.
After his really bad day at school, Mitchell's aunt mentions his father had come down with Poison Oak. His parents are supposed to be doing research in Australia, but both varieties of poison oak are found only in the United States.