Can we get a dialog option to flirt with the Crystal Exarch? [mild spoiler]

[Iscah]

I also got the impression that he was immortal due to his bond with the tower, and he may not be physically aging at all.

His white hair seems to be a side-effect of the crystal, not a sign that he's getting physically old - it's gone white at the tips rather than the roots.

I think he still had the grey hair when you saw him outside of the tower and he was with a descendant of biggs and they were finding lore/information about you in order to get things working again. Can anyone confirm?

It can't be confirmed - the scene is shown in first-person view, and avoids showing his right hand (which may mean he was already 'crystalising' at that point, or maybe they just want to keep us guessing).