In some recent studies, the origin of Indo-Europeans (both genetically and linguistically) can be traced back to Anatolia or more precisely Armenia. It’s even reported that the Etruscans (ancestors to Tuscans) also came from Anatolia and are confirmed as such. Armenian language and culture aren’t the oldest Indo-European civilisation but rather the oldest surviving one or the one still in existence.
It’s also one of the earliest countries to not only get Christianised but have it adopted as the official religion after a period of being under Iranian and Greek control. As what others said, it could’ve been as Muslim as Iran is nowadays. Zoroastrianism is also a monotheistic religion but despite being more biased to dogs than the three Abrahamic faiths it’s rapidly declining.
It was practised in Iran and to a lesser extent Armenia itself but not with much popularity and staying power as Islam and Christianity do. Armenia has also been subjected to Russian influence to varying degrees though one wonders if such influence extends not only to language but also to religion. It’s also safe to say it’s due to geographical proximity.