Compression socks are an “old people thing” (not necessarily*, but the association is there). So older trans people can easily buy themselves colorful, thigh-high compression socks and don’t even need to explain why.

*Actually compression jobs are great for people working desk jobs, because they prevent legs/feet from swelling during long hours.

I think it’s about gender stereotypes, the idea that long colorful socks are for girls, otherwise I would say it fits more under the non-specific category.