The Age cryptic by DH #20,525

I got this one done in a reasonable time for me (four hours) (shut up!) and there were no easy sides or themes or much here. Plenty of anagrams to get the puzzle opened up and it was good practice but not much stood out as fun. Am I spoiled to want fun? You can say yes.

That said I still have many gaps and five not fully parsed. Here's the pic:

9A - "Stevens returning it", states old Roman historian (7)

I'm pretty certain there's a homophone at play here but I can't figure it out. I googled "Roman historians" and from the three choices google listed I put in TACITUS from the cross letters.

23A - George to show off white of egg? (5)

The answer is GLAIR and I know the "George" = G but I don't know where the LAIR comes from. I could say "show" = AIR which leaves me with only the L unparsed. This isn't a word I'd heard before and I used One Across to help me out.

6D - Artificial surgical opening as Tom collapsed (5)

The answer I put in is STOMA.  I'm confident in my cross letters. I got a definition of pores in the skin but that's not "artificial" so I don't get this.  I was thinking it should be like an incision. I think it's "as tom collapsed" as fodder and anagrind but the "surgical opening" could be an S and the rest is something else. A Twitter friend got the same so I guess it's ok - I just don't like it very much. OK - I looked a couple of other definition sites and yes it works, I'm just new to the whole world of stomas and it seemed like it was something else than I thought it was - sorry.

14D - Companion learning everybody coming back common green alga (9)

The answer is CHLORELLA and I don't know where we get the CHLORE from "companion learning" but I do see "everybody coming back" = ALL reversed. Even if "learning" = LORE how does "companion" = CH?

17D - I am following Ivanovic and that guy in Disneyland area (7)

Answer is ANAHEIM and I know the "Ivanovic" = ANA is for the tennis player Ana Ivanovic and "I am following" = IM going after other two elements. It's the "that guy" = HE bit I don't like. I'd have thought it should be HIM? Is that splitting hairs?

The other thing I couldn't see was the connection between the three ellipses clues 13A, 15A and 16A. I did take the answers  IPSO FACTO, SWAMI and EXACT and mixed them up to get several hundred possibilities but COWE MAFIA SPATS TOXIC stood out but I'm sure isn't anything at all to do with me. Anyone suss out the triple link or was this an ellipses clue set with no link - that would be terrible and bad.

I've got Wednesday's printed and will dig in but I do not know much about opera so I may give up and go swimming at the beach instead.

As always if you want a clue broken down in more detail just ask in the comments or if you have better solutions please share them.

Happy Hump Day.