'Who was the youngest person' vs 'What was the youngest person'

[Honorfield]

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", question 9

......... was the youngest person to be elected President of the United States?

(a) Which
(b) What
(c) Where
(d) Who

English Grammar Tests, Elementary Level

ESL/EFL Test #93 "Why Questions", answer 9

Who was the youngest person to be elected President of the United States?

Correct answer: (d) Who

Your answer was: incorrect
What was the youngest person to be elected President of the United States?
_________________________

Hey there.
Why can't i use "what" in this case?

[Mister Micawber]

We do not use 'what' to refer to a person.
_________________
Native English teacher at Mister Micawber's

[Alan]

Hi Honorfield,

If you wanted to use 'what', you would have to say: What was the name of ...?

Alan
_________________
English as a Second Language
You can read my ESL story Present Simple

[Honorfield]

Thanks guys!