[CHOMAT]

Whenever there is past location that is the event is located in the past( use of an explicit date in the past, or using past tense) . In your example , were living "sticks" the event to the past. The present perfect does not work when the event is located in the past. Its modal value entails a mental movement from the past to the present ( values such as result, report, explanation of some deed). Remember those temporal locators belong to the field of language and mental represention ( tense and time) .

It is the first time + p. perfect : It is locates the utterance in the present . Unlikewise , here,preterit can't work. An other explanation: Present perfect enables the utterer to remember whether he/she has ever tried it sincehis birth/her birth ( for example) up to the moment he/she utters It is the first time...