Putting politics aside … Why don’t they have an age limit on the president (or any elected office)? E.g., you must be younger than the average life expectancy (currently men: 73yo / female: 79) - while in office. https://www.ssa.gov/oact/STATS/table4c6.html
There is a lower limit but not an upper limit. Who knows how old we can be in the future, there are coherent smart people over 80 today. But hey, it’s a democracy and if you want to change it you can try…!
Read as "who knows how much more entrenched future politicians will be able to be? who knows how many more favors they will owe, how many more donors will have their ear?"