I don't know if you want to look at "the Brady's of the world" as a GM when you do these kinds of things.
Counting on someone playing at a high level into their 40s is pretty risky taters.
True, but the rules today are _much better_ for QB longevity. Nutrition and fitness is more common and better than in the past. Staff monitoring of health and fitness is _much better_ than any point in the past, and enables good decisions way earlier. It is not uncommon for guys to last into their 40's today compared to previous times. And 43 isn't much into the fourth decade, and by the time that time comes, I think Stafford will still have a very strong arm and able to compete.
Today, the limiter is durability, so bigger QB's and ones that take less hits fare better. Stafford is an ironman type of QB, so he is a definite PLUS Durability guy ... and in a big way. His experience should help him play better as he ages. So, the chances are he improves with age and does play into his 40's, with a very realistic likelihood of hitting the 10 year number of 43.
The bigger question is whether you believe the GM is going to last 10 years. There's actually a lot more data that says no, the GM will not be there in 10 years. So with those considerations ... I see why absolutely no GM is really worried about how many years Stafford has left. They're just going to be interested in whether he can make your team win and possibly get the GM to the 7 or 10 year mark. Honestly, I think Stafford does it. The only negatives are 1) Coach needs to reduce the INT's, and 2) they paid a king's ransom in two 1sts (2022, 2023) and a 3rd (2021).
The GM will either be gone because it isn't a success within 2 years and they've lost the 2022 and 2023 picks in the 1st round, the GM will be fired and looking for a scouting job elsewhere. OR, it works and the GM is viewed as having a feather in his cap for finding Stafford.