The youngest established religion in Asia is probably Islam. Christianity was established in southern India by Saint Mark [he of the Gospel by the same name].
The oldest religion in Asia and indeed in the entire world is Hinduism, which is about 10,000 years old. Why has Hinduism survived for so long? Because it is very adaptable and accepting of new ideas, but not those which would allow an injustice to take place in the eyes of God
Hinduism is not a religion....its a name given to native Indians by Mid east people..... its used to be offensive like (meant to be like thug or ......Saki) now its a religion....
Islam is about 1400 years old, Christianity is about 2000 years old, Buddhism is about 2500 years old, Jainism is about 3000 years old, Hinduism(Shaivanism,Vaishnavism,Shaktism, Brahmanism) is about 3000 years old, Zoroastrians is about 3000 years old, Confucianism, Taoism is about 2500 years old. Sikhism is about 500 years old. Sikhism is the youngest religion of Asia.
If we take these religions as they are currently understood, then Taoism is the oldest, followed by Buddhism, Christianity, and then Islam.
Hinduism as it exists today, did not become as such until after Buddhism. Therefore it is NOT the oldest religion, even if its sacred texts are among the oldest in the world.