About Brandon Weeden's age, you have to break it down two ways. The first is the issue of longevity. You have to remember that the very first reason even a 29 year old quarterback ends up not playing very many games is not because of age but because of SKILL. If you're not good, you're not going to stay on the field. Success will be fleeting, and teams will get tired of waiting for you to recreate any success you had, or if you didn't have any to begin with them you're probably on a short leash and cycled right out of town.
So you have to start with the quarterbacks that were GOOD, and didn't really get their career going until their late 20's, and see how long they played. I look at guys that have completed over 1000 passes in their career, didn't get their starting careers really up and running until their late 20's, and have been to at least one Pro Bowl.
Quarterback - Age Started - # of Games - # of Pro Bowls
Warren Moon - Age 28 - 203 Starts - 9 Pro Bowls
Len Dawson - Age 27 - 157 Starts - 7 Pro Bowls
Steve Young - Age 30 - 114 Starts - 7 Pro Bowls
Roger Staubach - Age 29 - 110 Starts - 6 Pro Bowls
Daryle Lamonica - Age 26 - 84 Starts - 5 Pro Bowls
Sonny Jurgenson - Age 27 - 144 Starts - 5 Pro Bowls
Jim Kelly - Age 26 - 160 Starts - 5 Pro Bowls
Jeff Garcia - Age 29 - 116 Starts - 4 Pro Bowls
Kenny Stabler - Age 28 - 144 Starts - 4 Pro Bowls
Kurt Warner - Age 28 - 116 Starts - 4 Pro Bowls
Trent Green - Age 28 - 113 Starts - 2 Pro Bowls
Brad Johnson - Age 28 - 125 Starts - 2 Pro Bowls
Joe Theismann - Age 27 - 124 Starts - 2 Pro Bowls
Charlie Conerly - Age 27 - 107 Starts - 2 Pro Bowls
Mark Rypien - Age 26 - 78 Starts - 2 Pro Bowls
Jeff Hostetler - Age 30 - 79 Starts - 1 Pro Bowl
Jake Delhomme - Age 28 - 96 Starts - 1 Pro Bowl
Billy Kilmer - Age 28 - 114 Starts - 1 Pro Bowl
Danny White - Age 28 - 95 Starts - 1 Pro Bowl
Bill Kenney - Age 26 - 74 Starts - 1 Pro Bowl
Ron Jaworski - Age 26 - 140 Starts - 1 Pro Bowl
The average age involved here is 28 years old. The average number of starts involved is 119, which is between 7 and 8 full seasons which I call at about 8 seasons given some seasons you don't always play every single game. The average number of Pro Bowls is right between 3 and 4 Pro Bowls. This study frames what you can expect from Brandon Weeden's career, IF HE IS GOOD. What you have is proof that just because you got started in your late 20's, doesn't mean you can't make a big time contribution. You've got Hall of Famers on that list, guys that went to tons of Pro Bowls, Super Bowl champs, etc.
From there, I know some of you are going to say yeah but a lot of those guys were training in the NFL before they got those starts and so they could succeed right away. To that I reply 1) If you track all their careers, that's not necessarily the case, as many of them had a discernible learning curve, and 2) Look at the following second study.
This second study looks at guys that were drafted between 2001 and 2009 at the quarterback position, and played significantly in their rookie years (and 2nd years, and thereafter). What I tracked is their passer ratings as rookie passers, as well as their passer ratings as 2nd year players, as well as passer ratings in their full career.
Player - 1st Yr Rating - 2nd Yr Rating - Career Rating
Michael Vick - 62.7 - 81.6 - 80.1
David Carr - 62.8 - 69.5 - 74.9
Joey Harrington - 59.9 - 63.9 - 69.4
Patrick Ramsey - 71.8 - 75.8 - 74.9
Byron Leftwich - 73.0 - 82.2 - 79.7
Rex Grossman - 74.8 - 67.9 - 70.9
Kyle Boller - 62.4 - 70.9 - 69.5
Ben Roethlisberger - 98.1 - 98.6 - 92.6
Eli Manning - 55.4 - 75.9 - 82.1
Alex Smith - 40.8 - 74.8 - 76.1
Jason Campbell - 76.5 - 77.6 - 82.8
Kyle Orton - 59.7 - 73.9 - 79.3
Vince Young - 66.7 - 71.1 - 74.4
Matt Leinart - 74.0 - 61.9 - 71.6
Jay Cutler - 88.5 - 88.1 - 84.5
Tarvaris Jackson - 62.5 - 70.8 - 76.4
Trent Edwards - 70.4 - 85.4 - 75.4
Matt Ryan - 87.7 - 80.9 - 86.5
Joe Flacco - 80.3 - 88.9 - 85.6
Matt Stafford - 61.0 - 91.3 - 79.4
Mark Sanchez - 63.0 - 75.3 - 73.6
Josh Freeman - 59.9 - 95.9 - 79.5
Sam Bradford - 76.5 - 72.3 - 75.0
Tim Tebow - 82.1 - 87.9 - 85.9
Colt McCoy - 74.5 - 76.9 - 76.1
Average - 69.8 - 78.3 - 78.2
What you see there is that the NFL's learning curve has now shortened considerably compared with what everyone SAYS it is. But when people say that they're not basing it on anything concrete. The average passer rating in these players' 2nd years is actually slightly higher than their average career passer ratings. You have guys like Ben Roethlisberger that had better passer ratings as a rookie and 2nd year guy than he has in his time since then. Further, if you look at the 8 guys that are generally accepted to be franchise starters that people feel good about, about half of them made big impacts as rookies. You're also seeing that right now with guys like Cam Newton and Andy Dalton, and by season's end maybe even Christian Ponder and maybe even T.J. Yates. These guys are making big impacts as rookies.
So if you're looking at the 8 season average that you can expect a Brandon Weeden to play if he's a good player, you're not really shaving a season off that and chalking it up to a bad rookie year, because the chances are actually quite good (based on his skill set and maturity level) that he's going to be one of those guys that is able to impact right away. Andy Dalton, Cam Newton and Joe Flacco did not come from pro style offenses, or from anywhere that is NFL translatable. Heck, Joe Flacco played in a non-pro style system in the FCS not the FBS. If they can impact right away, so can Brandon Weeden.
So some people can keep just saying the line over and over again that a 28 year old isn't worth investing in, but they're doing very, very little to actually demonstrate that, whereas NFL history itself has gone a very long way to demonstrate that indeed a 28 year old highly talented passer prospect is worth investing in.