D+35 Differential between those under 45 relative to those over 45. I would point out that Griffin found similar differentials in 2014 exit polling in GA, TX, MS and SC.
Young white Southerners ARE NOT Republican enough to keep the GOP above water. Generational change will pull the top line white vote down and these states will flip. Alabama might take the longest of that group to flip though. This is not the suburban massacre like in Virginia (which was mixture of natural generation change and in migration), though it certainly will manifest in the suburbs. This is native generational change against the back drop of an immovable object, the Democratic Vote among African Americans.
The assumption there is that people do not get more conservative as they age. I would say that, while there are more conservative and more liberal generations, all generations become somewhat more Republican with age. Also, Alabama's electorate isn't significantly less white at younger ages (unlike most other places), and the other poll with Jones up suggested that Trump actually won 18-24s in Alabama by more than he won the state as a whole, but that there are a huge number of Trump-->Jones or Trump --> Undecided/Not Voting young Alabamians.
That should be no surprise - Moore’s appeal is definitely generational
Older voters either dont care and are solid republicans and/or think that it was the norm during their time so they dont care.