The phraseology is a bit dated, but it is still used.
Interested in Language
May I use phrases like she is ten years my junior or he is twenty years my senior without sounding obsolete? I am asking because I have found this junior/senior thing only in an older literature.
Thank you very much
Not a Teacher
You see it often in British news items when someone famous has married a new partner who is surprisingly a lot older, or younger, than themselves. Or perhaps when a sports veteran has competed against much younger athletes. in a charity race for instance.
***** NOT A TEACHER *****
To the best of my (very limited) knowledge, I do not think that you, a human being, can sound "obsolete."
I think that "obsolete" refers to things. For example: "Jupiter has agreed to sell its obsolete spaceships to Mars."
On the other hand, I would sound old-fashioned or out of date or behind the times if I were to tell someone:
"Wow! Your new car is the cat's meow!"
That's how "cool" people talked in the 1920s. ("Wow! Your new car is really great!")
It doesn't sound dated to me as I see and hear it in BrE in contexts like the ones given by Peedeebee.