You keep saying that people don't lose speed starting in their late 20s. Certainly by their early 30s. That is just untrue. Maybe it is only a tiny loss, but hardly anybody sets personal bests in the 30s in speed events. THE MARATHON IS DIFFERENT BECAUSE IT IS NOT A SPEED EVENT. Endurance is much more important there which makes it much more possible for a marathon runner to set a personal best in their 30s and even late 30s.
Your comment on Bolt is also misdirected. That interactive chart defaults to the best time for each individual. You can change it (button on upper right) to the best times period. Then you can see like Bolt's 20 best times and I think only 1 of them was after he was 26 or 27 years old. He peaked in his mid 20s like many great sprinters and was able to maintain his speed for another 5 years until he retired at age 30.
Each post of your throws out a name to make a case. This is argument by outlier. Show me average times for any broad set of runners and you will see that performance and speed declines after the late 20s and certainly by the early 30s.
Hurts is likely to see a decline in speed. Whether it makes him a mediocre quarterback is uncertain. He is a good quarterback now, but speed and the quality of his team around him (very good) are other factors in his good performance. RG III fell apart when he lost some speed. He is an extreme case, but his speed hid his other weaknesses. Put Hurts on the Commanders now and I'm not sure he'd do much better than Carson Wentz (the Commanders have a truly awful offensive line as we all saw a couple of weeks ago).
Teams matter. Tools (i.e. speed and arm strength) matter. And skills matter, It is hard to know what that adds up to yet with Hurts.