In his first year as a starter, Mahomes threw for 5,097 yards and 50 touchdowns in the regular season. Only Peyton Manning, who set NFL records with 5,477 yards passing and 55 touchdowns for Denver in 2013, topped both totals in the same season. Among second-year quarterbacks, only Dan Marino, who threw for 5,084 yards and 48 touchdowns for Miami in 1984, is even close.
Source: latimes.com – Los Angeles Times