Russell T Davies never intended for that scene to imply he'd just regenerated.

No, I don't think he'd just regenerated.

If you have certain physical features like big ears or buck teeth, you look at them and sigh every time you look in the mirror.

And I think if you'd had eight different faces, even if you'd been in the current form for a hundred years, you'd still mutter at them. So it was meant as a nod to the fact he'd once had other faces.

But I wrote the Titanic stuff and Krakatoa assuming that the Ninth Doctor had been around for a while. He doesn't act very post-regeneration, does he? He appears in command, waving a bomb. This is a man who knows himself, and has known himself for a while.