what is the oldest language in the world

Languages, especially living ones, are constantly changing so it is difficult to say what the oldest currently spoken language is because the ancestors of the people who speak it now would very likely have spoken in a way quite unrecognisable to people today, even though one could say that they spoke the 'same' language. In order to decide what answer you really want, it is necessary to define what you mean by "oldest language". Do you mean, for example, the first grunts and squeals of our ape-like ancestors or do you mean the language proper which is the earliest common ancestor of today's languages? Do you mean the oldest written language or, perhaps, the earliest written account of a language (two different things!)? The earliest attested account of a specific language seems to be a reference to Sumerian as having existed approximately 5000 years ago. No doubt there were older languages and many people claim that Sanskrit is one of the oldest languages (if not the oldest) but there is evidence that Sanskrit, Greek, Latin and nearly all European languages have their roots in a much earlier language or family of languages which have been lost and have no real name as such (though they are sometimes referred to as "proto-[something]" (from a Greek word meaning 'first in time').

I think the oldest language is Sumerian. It's one of the ancient languages but is not used anymore nowadays. Maybe you should look up on it.

it is Sanskrit. used by the Indo-Iranian people. Greek,Latin, Tamazight, Tamil and Hebrew are also some oldsters.