Quando iniciar frase interrogativa com At What?

Não são usadas preposições ao iniciar frases interrogativas, certo? Porém quando deve ser usado at what, como nos exemplos:
1 - At what age does she think people should get engaged?
2- At what age does he think people should start learning English?
Agradeço esclarecimento.

CENTENAS DE EXPRESSÕES DO INGLÊS
Preparamos um plano de estudos para ajudar você a dominar centenas de palavras e expressões do inglês em tempo recorde. EXPERIMENTE AGORA
1 resposta
PPAULO 6 49 1.3k
At what/at which age does... are fine by me. Some people would think of "which" as being about two options, or limited options, though.

But it doesn´t always work this way, one example of the use in a different way:
(At) what time does she get up every day?

It´s a bit of specific in kind, so one wouldn´t use "which" in such case.

Anyway, the point is that we can make questions with a preposition at the beginning of the sentence. So, the sentences you came up with are fine in English.