I'm not sure why the age discrepancy is so vast, and I'm also not sure where people are getting that FL's youth vote was in the single digits. Here's what I have in my exit poll spreadsheet for
18-29 year-olds (CBS exit poll):
Oklahoma 0.12
Alabama 0.14
Vermont 0.14
South Car. 0.15
Vermont 0.15
Mississippi 0.15
Ohio 0.15
Tennessee 0.15
Missouri 0.16
Virginia 0.16
North Car. 0.17
Florida 0.17
Illinois 0.17
Iowa 0.18
Nevada 0.18
Arkansas 0.18
New Hamp 0.19
Mass. 0.19
Michigan 0.19
Texas 0.20
The average across these states thus far is right at 17%. Including 30-34 year-olds would likely push that up to around 20%. I have no idea which other age group is being over-represented in the poll here, but I'll assume that it's a group that is anywhere from 55-70% Clinton.