This is highly subjective, but I'd consider Windows 7 as retro at this point. As of 2024, Windows 7 is 14 years old. Windows 95, for instance, was already 14 years old the year when Windows 7 was released (2009). And Windows 95 was already seen as "retro" by that time.
I am typing this on Windows 7 and lots of programs e.g. utorrent still produce new versions which run fine on Windows 7, so I'm thinking many of the older Windows APIs are still in use and haven't changed much.
Whereas Windows 95 vs Windows 7 are very different architecturally with one being clearly superior to the other, and also Windows 95 was at the start of its series and got more mature with Windows 98 etc. and Windows 7 was already mature.