Right age is 3. If a child is made join at 3 then for everything in the life will be done at correct age. like studies will complete by 25. can get marry at 27.
I think right time is after 3 years previously it was 5 year because there was no kg and nursury class.
Strictly speaking, kindergarten and nursery classes are pre-schooling and cannot be siad to be beginning of education. The lowest level of education is primary viz. class first to five. The entry in first class should not be at an age less than five years.
Though I believe that the right age for schooling is plus five as they are both physically and mentally developed to tackle the situation but I also find many children going to school now-a-days at the age of three plus...!