Ok, I got some crosstabs, sort of
18/34 years: 47/28 25% undecided
35/54 years: 45/37 18% undecided
55/74 years: 33/47 20% undecided
75+ years: 17/39 56% undecided
So it seems that the undecideds are rather good for the Dems, based on age alone. The 75 group is both worrying or promising, as they are rather D in the south, and are a split generation as a whole. The 55-74 form the GOP base, and its good that in the poll, Cruz already seems to be milking it, so its unlikely the margin can get bigger.
EDIT: I got the press release, though it doesnt have as much info as I would have liked.
https://www.emerson.edu/sites/default/files/Files/Academics/ecp-tx-aug2018-pr.pdf