Statement: It is desirable to put the child in school at the age of 4 as so.
Assumptions:
I. At that age the child reaches appropriate level of development and is ready to learn.
II. The schools do not admit children after 5yr of age.

If only I is implicit

According to the question,

As per the statement it only says about the desirable age of the child to put him in the school which is mentioned in the assumption I as child is mentally set up for learning and assumption II says about school policy which is not given in the statement.

Hence only assumption I is implicit.