@Subarna Das I dont have any problem regarding the schema is in 1nf or not I know that it is in 1nf.
My problem is that in the answer to this question it is written that the dependency (DOB -> age) is a partial dependency.
But if you see the definition given in navathe (written in the question) then (DOB-> age) is not a partial functional dependency.
Rather I think {DOB, NAME} -> age is a partial functional dependency.