It is so old that its past goes into pre-history.
The oldest Text is Rig Veda which is about years old. Hinduism is a religion that is dominant in South Asia. At this time, too, the Brahmanas—lengthy Sanskrit texts expounding priestly ritual and the myths behind it—were composed.
Most of the Puranas are predominantly sectarian in nature; the great Puranas and some subordinate Puranas are dedicated to the worship of Shiva or Vishnu or the Goddess, and several subordinate Puranas are devoted to Ganesha or Skanda or the sun.
Hinduism places third as an organized religion and is much older than Buddhism. Hanuman, the monkey god, appears in the Ramayana as the cunning assistant of Rama in the siege of Lanka.
Hinduism is a religion with no precise beginning.