When Kolb was an Eagles quarterback, Castillo was in charge of the offensive line, and Kolb said he clearly remembers the work ethic and results Castillo demanded.
So Kolb is prepared to at least match that preparation.
"No one works harder than Juan," Kolb said. "No one will outwork him, and I can see why Andy [Reid] selected Juan for the [defensive] job. With his preparation, we certainly have our work cut out for us."
Over the first two games this season, Kolb has put up better numbers and demonstrated a greater mobility from the pocket than he had with the Cards. His 95.7 quarterback rating for the first two games is much higher than the 81.1 percentage from his play in nine games last season.
So far, Kolb has completed 21 of 35 passes for 206 yards, two touchdowns and no interceptions.
"Overall, I like the position were are in and how we are playing," Kolb said of the Cardinals, who have won seven of their last nine starts dating back to last season.
"It's nice to get out with two wins, but we can't get too high or too low at this point in the season."
Against New England on Sunday, Kolb scored the winning touchdown on a 5-yard run one minute into the final period. Overall against the Patriots, he completed 15 of 27 passes for 140 yards and had a quarterback rating of 82.3.
Compared with Tom Brady's rating of 79.6 for the game, Kolb demonstrated he can handle an offense deep in receivers and competent in the running game.
"We did what we needed to do," Kolb said of Sunday's win. "To continue to win, we need to hold on to the ball and stay away from turnovers."
When the Eagles decided to go with Michael Vick as the starter before last season, Kolb became expendable. Dealt for defensive back Dominique Rodgers-Cromartie and a second-round pick in the 2012 draft, the Cardinals immediately signed Kolb to a six-year deal worth $63 million, $21 million guaranteed.
While fans and the media may suggest that Kolb has great incentive to beat the team that gave up on him, Cardinals coach Ken Whisenhunt dismisses the notion.
"I don't really buy into the theory a player wants to do well against a former club," Whisenhunt said. "I know [Kevin] wants to, but that's human nature."
Last season, the Eagles were also on the Arizona schedule, but Kolb was forced to the sidelines with turf toe and a bone bruise. Essentially, he spent the final two months of the 2011 season battling the two injuries as well as head trauma and lost his starting job.
Reserve John Skelton stepped and guided the Cardinals to a successful second half, and Kolb never recovered to win back his starting job. Then Skelton went down with a high ankle sprain in the second half of the season opener against Seattle. Kolb took over and since has guided the Cardinals to consecutive victories. The last time the Cardinals started 2-0 was 2008.
Now, the 28-year-old Kolb faces an Eagles club also undefeated at 2-0. While Whisenhunt told reporters on Monday, "We are very close to being a very good offensive team," the burden is on Kolb to validate that observation.
Fortunately for Kolb, he has help. Wide receiver Andre Roberts already has two touchdown catches, and star Larry Fitzgerald, with five catches for 67 yards, started his prep work Sunday night.
"On the plane [back from New England], I studied [the Eagles] preseason games and the first two games so far," Fitzgerald said.
"The Eagles are an extremely talented team and one of the best. This will be a really, really tough game for us."