I don't know, but Aaron Rodgers had the time to work on his throwing motion, and look where he's now.
http://thesidelineview.com/columns/nfl/can-quarterbacks-mechanics-be-altered
Had he been thrown in early like Bortles, he wouldn't have had time for that. It's not the easiest thing to fix.
They're still trying to fix Bortles' this offseason.
A bad habit can, and usually gets worse over the years.
According to Bill Walsh, it took Montana a few years to comfortably go trough all the progression (I read the book, but don't remember the exact number).
Montana sat and watched DeBerg suffered through a 2-win season as a rookie, and started just 7 games his second season.
And this was one of the smartest QB ever.
When he finally took over the reign in his third year, guess what happened?
The Niners won 5 games more than they did the previous two years combined, not counting the three in the playoffs that netted them a Lombardi.