Gil Brandt is still living in 1976. I don't take anything he says as gospel. There are plenty of examples of QBs age 33 or older disproving Brandt's theory.
- Rich Gannon had his best years after 33. In fact, his highest season completion percentage and lowest INTs per pass attempt of his career was when he was 37.
- John Elway never completed over 60% of his passes in a season until he turned 33 and he did it three season post age 33. He also threw the most INTs of his career when he was 25, his second most when he was 28, his third most when he was 29, and fourth most when he was 32. His lowest INTs rate for a season was 10. He had that few of numbers of INTs three times in his career (ages 33, 34, and 38).
- Marino's second and third highest season completion rates were at ages 34 and 33. He threw the third fewest INTs in a season at age 35.
- Fran Tarkenton only completed over 60% of his passes in a season five times in his career. All of them were when he was 33 or older. He had his lowest INT rare in a single season when he was 35 (tied for the season when he was 29)
- Joe Montana only had a single season completion rate over 70% once in his career (well twice if you count the season where he had a season ending injury in the first game of the season) and that was at age 33.
- Warren Moon had his highest completion percentage at age 36 and second highest at age 39.
- Vinny Testeverde had his highest completion percentage and lowest INT rate (for a season he played 14 or more games) at age 35.
- Last year Kurt Warner had his third highest completion percentage and second lowest INT rate as a full time starter at age 37.