in region 8, L7/8 regionals has a fixed number of slots which is divided up based on percentage of gymnasts in each state achieving a certain score during the meet season. the states with more gymnasts scoring above 34 get more slots. For instance, this past year, an NC had around 45 slots whereas FL had around 60. L8 works the same way but there are more slots available. NC had around 60.
From there, I am not sure if the states get to choose how to divide their spots but in NC, the slots are given to the top scoring gymnasts across all age divisions, not a certain # for age division.
And you are right, you need to a high score for L7, at least in NC. Lowest score to make the cut here was 37.3. L8 was lower with a mid 36, I believe.