So we have Hinduism, Buddhism, Judaism, all older than Christianity.

There is Zoroastrianism too and these are just some of the older religions that are still practised.

Sumerian religion is no longer practised but many of its stories are found in the newer religions so perhaps is still relevant.
That goes back to 5000 bce and prehistory.

Never mind, Christianity seems to be older than Islam, not that that fact makes it any more valid.