Jenny is younger than Lola. In the movie, she says that she skipped the 8th grade, and Lola says "you were the nerdy sophomore in my SENIOR chemistry class" So, if Jenny was a sophomore when Lola was a senior, Lola is TWO YEARS YOUNGER than her.
Don’t you mean that she is 3 years younger? Because Jenny skipped a grade. Therefore if she was a sophmore when Lola was a senior, then everyone else in her class would be two years younger than Lola, but since she is a year younger than everyone else in her class, then she would be three years younger than Lola, and she would be 16 but be a senior in high school.