According to Internet's aging speed and ability to move on to something else, I'd say... a month? 🙃
Seriously though, I'd say, a game you played during your childhood, if you're an adult in your thirties, could be considered retro. So, let's say, 15-20 years?
Will you still play videogames when you are retired?
Alloy from Horizeon Zereon Downeon (Idk why I wrote it this way, don't ask)
Easily forgotten but I found her well-written, she's kinda sweet and kinda strong, not overly aggressive, just the kind of strong human I like.