(im not a worker of nicec00lkidd or something and i don't work for the ESRB and other company!)
so nobody nows what's the age but in the main page ( which you can see it on Foxo's Fun Schoolhouse DEMO by Nicec00lkidd )
the is for This game is intended for players 13 years and older like what it say
but if is what's rated. like in north america is rated :
(Age of 13 +)
in other like europe is it rated :
Germany:
(Age of 12+)
UK :
(Age of 12+)
for learn more about other country you find it on this wiki : AGE ON EVERY COUNTRY