There are 3 quarterbacks
During the 1940 season the Bears carried 5 quarterbacks on their roster.
25 players are active during the season.
6
During the regular season teams will usually have three QBs on the roster and all three will dress on game day.
Tom Brady
20
Quarterback trades during a season are relatively rare in the NFL, but they do occur. Historically, there have been a handful of notable instances, with the number typically ranging from a few to around ten trades per season, depending on the year and circumstances. Some prominent examples include trades of quarterbacks like Jimmy Garoppolo and Sam Darnold. However, the exact number can vary significantly each season.
4
2
None. Brett Favre is the oldest active quarterback at this time.
During the regular season, there can only be 12 active players. so 36 players. However, there can be more, just not all of them will be active.
There are no quarterbacks over 40 who are currently on a team. Brad Johnson, who is currently a free agent, is 40 years old which makes him the oldest quarterback in the league. Kurt Warner at age 37 is the oldest player currently on a team.