The current ATP ranking system goes back until 1973 with a total of 25 players being ranked #1. Currently Novak Djokovic firmly holds the distinction of #1 in the world. But as Djokovic ages, how long could he realistically hold on to this top ranking. Below is a chart of all former #1 players and their time at #1 against their age.
From this chart, there have only been 2 players to have a lengthy hold on the top spot after the age of 29 ( Lendl & Agassi) and even then that hold only lasted only about age 30. Does this mean that Djokovic has at a maximum of 2 years left as a clear #1 ranked player. Well that depends on if Djokovic follows the trajectory of all the former number 1’s. However, with his current fitness level perhaps he will be an outlier.
Another way to slice the data is look at the age of the ATP #1 vs time.
If one follows the blue line, it is clear that age of the number follows a trend of starting in the low 20’s and continuing up until around 30 before resetting again. This can clearly be overlapped by eras in men’s tennis.
Many tennis experts are writing & talking about the inevitable transition to a new generation of players. History shows this transition may still take a couple years and will likely go to a generation of players currently around 20 years old.