An actress in her 50s or 60s needn't look ancient, of course. I was invoking the Maiden/Mother/Crone dynamic of goddesses and fairy tales, not suggesting that Thuringwethil be a completely wizened old woman.
Ming-Na Wen (Melinda May on Agents of SHIELD) was born in 1963, making her currently 53 years old.
http://www.imdb.com/name/nm0001840/?ref_=tt_cl_t2
This photo is from the Dr. Strange premiere (so, current):
Rene Russo (Frigga in the Thor films) was born in 1954 and will be 63 next month. (Photo below is from the 2015 Oscars)
http://www.imdb.com/name/nm0000623/?ref_=tt_cl_t14
Tilda Swinton is 56 years old. No idea what is going on in the photo below, but I think she would enjoy wearing Thuringwethil's costume, at any rate!
http://www.imdb.com/name/nm0842770/?ref_=nv_sr_1
Now, obviously, when reach that age I do, look as good I'll not. These are women who *are* older, but most certainly *look* younger. So, there would be some question of whether we're trying to cast an older actress, or whether we want the character to show some signs of age.
There are actresses who, while looking amazing for their age, don't pass as young/middle aged any more, and are only going to be cast for older roles. If we want to cast any of them in this project, we are going to have to give some thought as to when/where/how we'd fit them in.
Examples:
Helen Mirren (born 1945)
http://www.imdb.com/name/nm0000545/?ref_=nv_sr_1
Jessica Walter (born 1941) - She was Lucille Bluth in 'Arrested Development,' a mother of adult children and grandmother of teens.
http://www.imdb.com/name/nm0910055/?ref_=tt_cl_t9
Meryl Streep (born 1949) - Her Witch in 'Into the Woods' fits the Crone type, definitely.
http://www.imdb.com/name/nm0000658/?ref_=nv_sr_1