This article from an Indian newspaper puts together a bunch of sources on the question of beef eating.

It looks like beef eating was discouraged in Vedic times, with regard to cows that were yielding milk, but not prohibited, with non-milk producing cattle (e.g. bulls, oxen and older cows) valid for consumption, at least as part of a sacrifice.

Into the Mauryan era when Buddhism was dominant in India, the Emperor Asoka's laws likewise allowed the killing of sterile or aged cattle for food. One of the sources in the above article suggests that the Brahminical injunctions against any cattle slaughter, as opposed to just milk producing cows, was developed as a way to differentiate themselves from the Buddhists of the time.

It's notable that in Kerala in South India which was one of the last historical areas on mainland India where Buddhism remained competitive into the early centuries AD, alongside an early Christian community, beef is still widely consumed, even by some Hindus.