I'm going to show that not only was John Stockton was an outlier in terms of playing into a late age, but that Stockton's aging pattern is superhuman compared to the rest of the NBA. The way I'm going to do that is to show the best seasons in NBA history for players for each age group who was 6' 5" or shorter. Tell me if you notice a pattern in each list.
Top Seasons by age, Min. 1,000 MP. 6' 5" or shorter
Age 32

Age 33

Age 34

Age 35

Age 36

Age 37

Age 38

Age 39

Age 40

Note: Stockton is the only player who even played 1,000 minutes at age 40. In fact, there were only 2 other players who even played a single minute at age 40 (Jason Terry, John Long).
In EVERY single age from 32 and up, Stockton was the best player of that age group. 9 years in a row. Stockton's length of his career plus his level of play was unprecedented. No one was playing at that high of a level into their late 30's. As the age groups progress, Stockton's peers continually drop off in performance while Stockton stays the same.
Here is a list of the top seasons at age 33 or more for players who were 6' 5" or shorter.

Stockton has the 7 best, and 8 out of top 9 best seasons for any player over the age 33. Stockton at age 39 was BETTER than any guard in history who was 33, 34, 35, 36, 37, 38, 39, or 40 years old. Stockton at age 40 was so good that he was better than any age 33+ Guard season in history outside of 1 Gary Payton season. As I mentioned above, Stockton was doing that at an age where only 2 players even played a single minute. Playing at age 40 is impressive feat. Doing that while outproducing all of the players who are 7 years younger than you is impressive on another level.
I was being very generous with the height filters from above. When you get to players of Stockton's height 6' 1" and shorter, it's only him and CP3 who played well past the age of 33. The next most productive guards at that height are Mark Jackson and Darrell Armstrong. The pickings get very slim when you reach Stockton's height. That's why CP3's current run is impressive too. 6 footers aren't supposed to age well in the NBA. When 7 footers age, they get slower. But, they make up for that with height since you can't get shorter. 6 footers who lose their speed have nothing left to provide.
Here are the ages of the last all-star seasons for some notable PG's
Rose 23
Penny 26
KJ 27
Price 29
Isiah 31
Magic 31
Hardaway 31
Oscar 33
Payton 34
Iverson 34
Kidd 36
Nash 37
Stockton 37
Most of those players peaked early and aged fast. Only Kidd and Nash can compare to Stockton in terms of longevity.