I see some Wahl nibs marked simply "WAHL X", where X is the nib number, and others with an added "14k". Which nibs are older ?

here is a very quick overview of nibs and date ranges. the Wahl and Wahl Eversharp nib subject is mor involved that this but it may help to answer this question quickly.

Nib inscriptions from oldest to newest:

WAHL TEMPOINT # (c. 1918,19,20)

WAHL PEN #(c. 1921,22,23) tal

WAHL # ????? Still checking. I have these nibs too, This simple marking is "undocumented" in the catalogs, and adverts of the day. It may have been an after market Wahl manufactured nib supplied to dealers for repair, or perhaps a knock-off, sold to dealers for repair by others than wahl. My guess is that it was available after the tempoints and before the Gold Seals, but can not pin it down yet.

Wahl # 14K (c.1924,25, 26,27,28)

Wahl Signature (c.1927,28) This was their "semi-flex" nib in the nib range of this era and was specially marked that way

Wahl Eversharp Gold Seal (c.1929+++

And Wahl made a "point" of calling their tips "osm
iridium, the hardest substance know" Here is a very shor-hand version for simplicity

Dont know why the post cut a word in two but the tipping material was
"Osmiridium.

Thanks Syd. I've seen the "WAHL #" simple marking on several "All Metal Fountain Pen", such as the one I have, that you dated 1921-22ish.