Retro gaming consoles are on-topic, so it makes sense that retro games should be too.
In proposal some people voted against games though, so I'm asking to make sure we agree.
Questions about game play are likely off-topic, I feel. There is a huge gamer community online to draw on that is about gaming specifically, not necessarily in a retro manner.
Even Wikipedia refers to the ancient gamer stuff that is easily available as "game cruft", as it is very abundant (and nearly impossible to verify, sometimes.)
So, questions related only to game play probably already have a home out there. A question about getting a system, emulated or not, working so a game can be launched is probably on-topic.
For example, I consider getting Wumpus working on some emulators sort of an acid test.
Games from the past in itself are likely too broad a topic and would water the focus of this site too much. What I mean are questions like "How do I perform special move X in game Y", "How do I get endless lives in game A", "Was game B the first of its kind or were there similar games before" or something like that, which do not at all or only peripherally touch on the technical details of the particular retro platforms. Those are likely better asked on https://gaming.stackexchange.com/.
What is fine, in my opinion, is using them as examples to make the problem more concrete, like in the questions Did any Amiga 500 games or programs (apart from paint programs) use more than 32 colours?, Is there way to save the save state? or GameBoy Color games do not save any more.
The focus in those questions is clearly the methodology used on the platform, not the actual games in particular.
However, if the question to a particular game of the past doesn't fit into https://gaming.stackexchange.com/ at all, then it might be fine to ask it here. I guess that depends on the question on a case by case basis.
The tricky part with your test case is that it's not obvious from the question whether you're asking how to play the game or how to get it to work on the specific retro system in question. It's especially tricky because it wouldn't necessarily be obvious to the person asking the question, either. If they had access to multiple systems, and posted "it works on my ][+ but not on my //e", that would be a very strong signal that there's an issue with the platform itself.
I think the biggest problem with the question is the subject, "How do I become a Space Ace in Ultima I?", which sets the tone for the reviewer. Unless I'm aware of the coding flaw in Ultima I my assumption will be that you're asking about game play, and assuming that PEBKAC.
If your subject and question had the tone, "I'm doing things that should work, but they're behaving incorrectly on my //e", that sends a message to the reader that you're looking for help diagnosing strange behavior, rather than seeking to learn how to become a Space Ace.
I dislike the idea of rejecting valid questions because the asker didn't have enough experience to frame the question well, but until the asker has enough knowledge of the situation to identify that something retro-platform-specific is at fault, they shouldn't really be asking gaming questions here.