Statement: It is desirable to put the child in school at the age of 5 year or so. Assumptions: 

I. At that age the child reaches appropriate level of development and is ready to learn 

II. The school do not admit children after six years of age.

Since the statement talks of putting the child in school at the age of 5, it means that the child is mentally prepared for the same at this age. So, I is implicit But. possible to nothing about admission after 6 years of age mention in the statement. So II is not implict.