I can't remember when I read Dune - would have been quite young I think, I remember reading Silmarillion around 11-12, as was a book at the school library at the time, which was for when I was 11-12, and had read LOTR / hobbit before that some time, and I think Dune around the same sort of time.
Wheel of Time was later as only discovered it when 17, but I think I could have easily read it earlier.
I read Hobbit / Lord of the Rings / Silmarillion to my now 12 year old, over a couple of years and finished months ago, so likely a chunk of LOTR at 10, and while was listening rather than reading, still followed it well.
My 14 year old was reading LOTR around 12, and now 14 is currently reading Unfinished Tales, planning on going to History of Middle Earth next.
So I don't see issues with someone reading Wheel of Time at 14 - she is enjoying the TV series, and while I Suggested not reading the book until finished the series, as may spoil it (in more ways than one), I think she would happily read it after.