Looking up the term "oldware" online, it is actually used by some sites, namely ones that also deal in abandonware, as a portmanteau to refer to "old ware". It's also the name of one site that deals in it. However, there are a much larger number of sites dealing in the same content that do not use the term, and there's also an Old Ware Rd over in Alaska.
It's an intuitive tag to understand when you see it. I don't think it's an intuitive tag for thinking about what tags to apply to a question, though. The term's low frequency of use for the subject means that it's not going to pop into a lot of people's heads when they're trying to tag a question. So I support that we retag it to [old-games]. Likewise, I support the plural version since the category best fits as "Questions about old games" than "Questions about an old game".
Update With help from ChrisF, this job has been completed.