I’ve read many hiker journals - Comer & Jean, for starters - who have thru-hiked starting in December/January. And they manage just fine.
You know that photo of Bono and Rocket that appears fairly often on the home page of trailjournals.com? Bono started in December. Read his journal if you want to get an idea of what you’ll encounter in terms of weather or resupply (And Comer & Jean’s). Better yet, email them directly.
My reason that I’ve read so much of these early season nobos is because that might be my only option to thru-hike (unless I quit my job).
Plan B would be to hike southbound, starting at Katahdin in September (about the second week) and just haulin’ ass before the Whites do their thing.
NOBODY that I’ve read has ever done this type of thru-hike. Not on an online journal. There is an old book with an account of Jim Shattuck’s sobo, though he started in late August (but he hiked a bit slow, and as far as I can figure, I’d have caught up to him).
ALSO! TDS - Totally Different Subject - went as far as Deleware Water Gap, starting at just the same time as me (September 10 - he was flip-flopping, I was lolly-gagging).
These guys who tell you not to go . . . hike your own hike. There are much more than a few hikers who have done it.
Kineo Kid