The start of the N.F.L. season was a rough one for some of the league’s most bankable quarterbacks. Andrew Luck retired before the start of the season. Drew Brees hurt his thumb and will be out another month or so. Ben Roethlisberger is done for the season because of an elbow injury. Eli Manning, the cornerstone of the Giants since 2004, was replaced by a rookie, Daniel Jones.

But as the N.F.L. rolled through its fourth week, the league’s quarterback corps, by necessity or design, has gotten younger in a hurry — with mixed, and sometimes exciting, results. Through Sunday night’s game between the Dallas Cowboys and the New Orleans Saints, quarterbacks 26 or younger have started 52 games this season, breaking the record of 48 in the first four weeks of the 1987 season.

Young players can infuse new energy into teams and breathe life into seasons ready to skid off the rails, as Gardner Minshew in Jacksonville (2-2) and Jones in New York (2-2) have done. Other quarterbacks, like Josh Rosen in Miami and Dwayne Haskins in Washington, are works in progress.

Then there are established 26-year-olds like Dak Prescott of the Cowboys and Teddy Bridgewater of the Saints, who faced off in New Orleans on Sunday night. Prescott is off to a fast start, completing nearly three-quarters of his passes, a big reason the Cowboys won their first three games. Bridgewater, who stepped into Brees’s big shoes, led the Saints to an upset in Seattle against the Seahawks last week.