Word of caution: young voters make up too large a portion of the electorate in AZ and IN in these (15-17% under 30 lol...). Florida looks about right demographically (12%, which might still be high but isn’t unreasonable).
Why would you think 12% might be too high for the 18-29 cohort? If anything, it seems too low to me.
According to exit polls in Florida, 18-29 constituted 14% of the electorate in 2014 and 17% of the electorate in 2016. And Florida is older than the average state. I couldn't find exist polls in IN for 2016 or 2014, but in a 2012 exit poll, the IN electorate was 20% 18-29.
If anything, the IN poll is way too heavily weighted in favor of less educated voters. In the 2012 exit poll, the Indiana population was 44% college graduates and 24% no college. In this poll, it is 33% college grads and and 38% no college. I have little reason to believe a midterm electorate will be much less educated than a general electorate.
FWIW, the exit polls have long been known to over-sample college graduates.
That being said, midterm elections are exactly when college graduates would punch over their weight. Working class voters tend to experience a dropoff in midterms.