How old are Ishishi, Noshishi, and Zorori? I am mainly wondering about Zorori's age, I've seen a lot of the episodes and haven't found out yet. If you can, please give the episode number or the canon source that verifies your answer
In the anime, Zorori age was never mentioned.

However, in the manga, despite his young appearance, Zorori's age is over 120 years.


On volume 15, titled かいけつゾロリつかまる！！ (Kaiketsu Zorori Tsukamaru!!, "Kaiketsu Zorori Arrested!!"), there's a newspaper about his fugitive warrant with the text 「かいけつゾロリ(109)」 (Kaiketsu Zorori (109)), which means that he was 109 years old at that time. (source: hensachi60's tweet (Japanese))
On volume 46, titled かいけつゾロリ きょうふのようかいえんそく (Kaiketsu Zorori Kyōfu no Youkai Ensoku, "Kaiketsu Zorori, the Terrifying Monster Field Trip"), it's mentioned that his age was 124 years old. (source: Yahoo! Chiebukuro (Japanese))
In the spin-off manga series, ほうれんそうマン (Hourensou Man, Spinach Man), the 1st volume, titled へんし〜んほうれんそうマン (Henshi~n Hourensou Man, Transform Spinach Man) has a scene of Zorori's 100th birthday. (source: Japanese Wikipedia).


The boar brothers Ishishi and Noshishi's ages, however, are never mentioned at all.



Reference:


Japanese Wikipedia
pixiv encyclopedia (Japanese)