I don't think you can put a proper number of years on to that, thta is decided by other factors that result in faster or slower "aging" of a title.

From the viewpoint of management, a remaster or remake is warranted, once it is conceivable, that it will sell well enough. Maybe new demographics entered gaming that never touched the game in the first place or the original is somewhat unavailable and therefore a remake might sell well.

For gamers that played the original game, that line might be different. Maybe they want all their games on their newest hardware. Backwards compatibility is one way for that, but remakes or remasters are another. But the major point are probably enhancements that improve the gaming experience. That can include, but is not limited, to graphics. For graphics we have good points what is still acceptable in old games and for what we like new stuff. For instance if the original wasn't HD, then a HD or 4K upgrade will do nicely. But there might be other things. Maybe the game had bugs or glitches that a remake tries to remove. Maybe the remake can add a mode, that can improve the original game. Or maybe simply the original game had great multiplayer, but the servers are no longer working and the remake brigns new servers.

So many things could define a remake worthy. I don't think it is easy to pinpoint it to something specific.

If they were remaking FFVII, I would have preferred more of giving the core game a Dragon Quest XI-style facelift, but otherwise sticking to the structure of the original.

I'd say if they are 2-3 gens or older. 360 era games didn't exactly age all that well, and as a result we got a few remasters/remakes from that era, and I'm pretty sure Dead Space started during the 360 era as well, so it makes sense that it's now two gens old now and fitting for a remake.

There isn't a rule tbh

The first Pokemon remake was released only 8 years after original

At least two console generations, and maybe more depending on the game. I haven't played Dead Space but my impression is that it's not in need of a remake just yet. On the other hand, someone mentioned Oblivion, and it's aged very poorly, to the point where it would benefit a lot from a remake. Going back even more for an opposing example, I don't think Doom 3 still needs a remake (although it too would benefit a bit from one).

Some say the Game needs to have gone Gold,but the truth is you need to at least wait for the day one patch/update otherwise it's to early.

I both love it and hate it.  I love that I can revisit the world and the characters with updated graphics and voice acting.  However, they really did butcher the story.  They also added a bunch of other content that is a lot worse.  It's both really fun and really disappointing at the same time.

I am kind of jealous of Xenoblade Chronicles fans.  They updated the original game in 2020 just like FF7.  They improved the visuals, added some extra content and kept everything else the same.  That is exactly the treatment that they should have given FF7.  They only made a small portion of the original game in the remake, because they wanted the most cutting edge graphics possible.  Screw that.  I would have been happy with Xenoblade Chronicles (Switch) or DQ11 level of graphics.  Both of those games are huge and look great to me.

My opinion on remakes has changed a lot over the past couple of years.

We simply consume media differently than we used to. Take a show like Avatar: The Last Airbender. In the old days it would have its run on Nickelodeon, they'd show the reruns for a few years, then it would be relegated to reruns at like midnight on some obscure channel for nostalgia purposes, while younger kids would be like "what's an Appa"?

Now, with Netflix, it's still fairly relevant and popular among a wide range of ages something like 15-20 years after its initial release. Outside of a few rare examples like Seinfeld, a show that hadn't been running new episodes for a decade wouldn't still be that relevant years later, but due to streaming, shows have a much longer lifespan.

The games industry is going the same way. Back in the before times, in the long long ago, a game would release on a console, and that would be it. Your Marios and Zeldas would get remade, but unless something was uberpopular, it would come, be forgotten, and go. Now, it gets polished up and rereleased every five years. It's not necessarily for the people who have already played it (although lots of people seem to be willing to buy the same game several times) it's more to reach a new audience. And of course those people COULD have simply gone to a used game store and picked it up, but you need to do something to bring it back to the store front, and also it needs to be sold through the new games market, or else developers have little incentive to bring spend marketing $s bringing back interest.

And I don't think it's necessarily a bad thing. It could mean companies rereleasing the same games over and over again, but it also incentivizes the creation of games that will stand the test of time. Before streaming, reality shows were dominating the TV market to a ridiculous extent. And while they're still prominent, streaming has helped reestablish the kinds of long terms shows people will be watching for some time to come, rather than shows like survivor or American Idol which few people are watching after their original run.

So, to answer the question, I don't think it has much to do with the visuals and it's not intrinsically linked to time. It really depends on the particulars of the game and how much it can potentially resonate with modern audiences. Undertale could have probably run on a SNES, but I'm fairly sure it will make its way to every console over the next two decades in largely the same form, because it's the type of game that will be able to appeal to new audiences for quite some time.

Xenoblade got a remake 10 years after but the hardware difference was huge. NES Super Mario games were remade on SNES and while they looked nicer did not improve them in any real way. I don't think a length really determines it but if new hardware offers enough power to make a real difference. Conker Live and Reloaded was a 4-year difference but Xbox made huge improvements visually. PS4 and PS3 are not a big enough gap for Dead Space in particular to make a real difference. PS5/XSX with RT can offer all kinds of lighting features in a horror game.

Its always a hard answer on this one. Remakes should happen on games that are at least 2 generations apart and that their is enough technology innovations that will be day and night different. Than again some games on the 360/PS3 don't need remakes 2 generations after so it comes down to the visual difference.

Games like Perfect Dark deserves a remake, games like Doom 3 don't. It really depends. Than again games like Dead Space i am excited for however that might be for other reasons.