Physicist: Normally this question is only used to start fights.
Some theories posit that the big bang was the beginning of everything, and that it doesn’t make sense to talk about anything earlier, while others say that it may be impossible for the universe to have a beginning or end. Both options are terrible.
We can track the progress of the universe all the way back to only moments after the big bang, but no further. So we’ll never actually be able to see what happened at the instant of the big bang. However, there are some pretty slick tools that allow us to extract results by studying the crap out of how spacetime behaves today. Notably the Hawking Singularity Theorem. We may be able to determine if the the big bang was a singularity (with nothing before), or just a severe “pinching” of the universe (with stuff happening before).
You can picture this as something like trying to figure out whether or not your sheets are pinned together in one place based on how they’re folded and bunched up in another place. It’s tricky.
However, for all practical purposes the universe is about 15 billion years old (give or take). If there was anything around before then, it got messed up good by the big bang.