Okay, then...

Violet Crawley, Isobel Crawley, Martha Levinson and Elsie Hughes from Downton Abbey. (I can find at least one older femslash pairing too: Isobel Crawley/Elsie Hughes). I'm not sure whether Cora Crawley's over 50 or not yet. I think she must be by now?

Jane Marple (Agatha Christie) Also Araidne Oliver (who does have a tag if no proper fic)

Connie James from Spooks/MI5 and Tessa Phillips

Mrs Hudson (BBC Sherlock)

Sandra Pullman (New Tricks)

M (as played by Dame Judi in the more recent Bond films).

Minerva McGonagall (Harry Potter)

Dolores Landingham (West Wing)

Harriet Jones, Evelyn Smythe and Amelia Rumford (Doctor Who)

Widow Lucas/Granny in Once Upon A Time.

There is a theory that the world is run by deceptively awesome older ladies. :-)