MySQL Unique indexing problem

When I went to the interview today, the interviewer asked a question about MySQL's unique index, assuming that there was a unique index User_uni (name,age) and deleted the column age, what would happen?

During the interview he said the column could be deleted, but there would be a problem with the query. However, after my verification, if the name column is duplicated, the age column is not deleted.

This is the data:

This is the index, as you can see, name and age have a unique index established:

When you try to delete the Age column, you are prompted to repeat the value

In addition, columns can be deleted normally when the data is not duplicated

MySQL Unique indexing problem