Vinny Testaverde
Fans paid tribute to Testaverde’s longevity after he finally retired in 2007 with the Panthers. He played for 21 seasons and accumulated the most losses by any quarterback in NFL history. Testaverde received a lot of opportunities because of his consistency (via Sportsnet).
But he suffered a natural drop-off toward the end of his career. The problem was that his age made him less effective and he endured injuries like torn Achilles tendons and strains. These prevented him from being the same player that he was in his prime as he held on for too long.