Brady is old and will inevitably decline at some point, but people forget that his velocity was never elite. His deeper passes have always been more about timing and touch than pure power, even in 2007 when slinging it to Randy Moss all day. People saying he was in physical decline in the Super Bowl are imagining a prime that never was.
His game has always been about timing and making the right reads, small movements within the pocket, and knowing when to bail on a busted play rather than forcing things. The throws themselves were rarely "wow" plays in the sense of being amazing athletic feats. It's why age has affected him relatively little so far. He's maybe the most "boring" great quarterback ever because it's all about fundamentals and the mental game.
Peyton Manning fell off a cliff in part because he never entirely got over the neck injury, so he was hanging by a thread during the entire comeback. The miracle is that it lasted as long as it did really. The bigger issue for Brady isn't decline in throwing power, but having an injury a 41 year old body simply can't come back from like it could at 31, or accumulating multiple smaller injuries that add up to a derailed season because he can't bounce back like he used to.