- Hard to comprehend/understand, but our Universe has been around since "ever". Our scientists talk about some billion years ago as the starting point, but it isn't difficult to realize that there's infinite time before any time interval that we speak about.
- Important caveat: If our Universe is indeed a simulation run by a very advanced civilization, then our Universe of course can have a finite starting point [the point where their video game was started]. However, the parent Universe in which folks of that advanced civilization live [assuming they themselves aren't a simulation of someone else] has been there since "ever".
- Mankind already spends so much of its time inside all sorts of video games, including as characters inside virtual reality games [virtual worlds] such as Second Life. Proof enough that people seek to "escape" real life and live a more ideal/exciting virtual life, even if for only a while. Perhaps some aspects of the real world aren't always good, and solace is achieved within the world of video games.
- Fair to assume that similarly the folks of that very advanced civilization sometimes want such an "escape". Maybe they have technology so that a dude in that civilization can implant his consciousness/mind/personality into a character inside the video game which we are [assuming we believe in the simulation hypothesis] and live a virtual life as a human being. Maybe all of us folks are actually "them" - our bodies are virtual and our perception/understanding of our minds is actually a subset of their actual/full consciousness [that is, each of us believes that we fully know our own minds, but perhaps we just can't access/feel/read/see those contents/portions of our minds which they've restricted our access to, and which belong solely to them and they do not want to make a part of the simulation]. Maybe they immensely enjoy playing in this world that they've designed. Maybe they've put concepts and phenomenon in this world that they dream of [or miss], like love or simplicity. Maybe due to incredible technological advancement those folks are so machine-like now that they just can't be simple or "cute" anymore.
- Lastly, we know about only till a few billion years back. But the real Universe has been around forever. So this "forever" is "enough" time for development that's far, far, far ahead of anything that we are or anything that we can imagine. So it's likely that there's a much, much, much superior civilization our there, and that we're simply their game, and that we might never encounter anyone else.
Update [Jan'17]: Just felt that it isn't necessary that we're a simulation. It could very well be that we are the "creation" of aliens. Maybe it's the aliens who discovered our Earth as a far-off planet suitable for life, and maybe it's them who planted the seeds of life here. Perhaps they're watching us all the time, but in a way that we can't detect their presence. So it ain't necessary that we're a simulation. Perhaps we exist at the same time as them, and maybe we are their creation.