The big difference between 2004 and 2008 was not turnout rate, but self-percieved party ID, which collapsed from D+1 to D+9. This time, though, even D+9 doesn’t look like it can save the Dems.
Note that Mitt Romney, like Donald Trump, simply did not appeal to young Republicans.

Of course, this poll comes from September. I expect the #s on election day to look the same.