Lemuel is Definitely an Ancient - Easter Egg
I was re watching Season 3, and caught something Louis says when describing Lemuel in 3x05: "He doesn't count time like it's a badge. I go nights not knowing where he is." It's not simply the words itself, but Jacob Anderson's delivery, as though Louis is equally appreciative of this mindset while being fascinated by it (possibly because he can't yet comprehend).
And to me, not only is that a mindset that makes more sense in a vampire who's been alive 6000+ years. But it's also reminiscent of a line from Khayman's chapter in Queen of the Damned:
>Yes, the moment, the moment was splendid. And the moment was all he ever had. After all, he would forget this time too, wouldn't he? These nights with their exquisite details would vanish from him; and in some even more complex and demanding future he would be loosed again, remembering only his name.
I know there are plenty of theories about Lemuel being Khayman or Seth, I'm not theorising anything new there, there's literally dozens of ancient vampires he could be. But I do think this is a hint that he's definitely an ancient rather than a younger one.