I found these using profootballreference's season finder. I am a big believer in y/pa ( yards per pass attempt), and ay/pa (adjusted yards per pass attempt), and also completion percentage to project quarterbacks long term.
Cam is on pace to be one of 2 quarterbacks to have 3 seasons of +7.8 y/pa during their first 3 seasons (minimum 6 starts)
Otto Graham is the other (HOF, retired in 1955)
Cam is on pace to be 1 of 2 quarterbacks to have +6.16 ay/pa during their first 3 seasons (minimum 6 starts)
Dan Marino is the other
13 others had 2 ... Peyton Manning, Matt Ryan, Carson Palmer, Roethlisberger, Rypien, Warner, Cutler, Esiason, Bulger, Kaepernick, RGIII, Jeff Garcia, Russel Wilson
Cam is on pace to be +6 AY/PA and +57% completion % in all of his first 3 seasons so far.
There are 23 other QBs with 4 or more seasons with those types of numbers during their first 6 seasons
Those 23 QBs, sorted by number of seasons:
Joe Flacco, Jeff Garcia, Jim Kelly, Dan Marino, Roethlisberger, Matt Ryan, Peyton Manning, Joe Montana, Marc Bulger, Mark Brunell, Troy Aikman, Tom Brady, Jason Campbell, Daunte Culpepper, Jay Cutler, Delhomme , Brett Favre, Bernie Kosar, Jim McMahon, Donovan McNabb, Carson Palmer, Philip Rivers, Tony Romo