Well... I think it was Queen Zeal, outside the Black Omen, in 2300 AD, who claims that "Lavos reigns from atop Death Peak" or something to that effect. Though you climb to the top and never see him, so... not sure what that's about.
I, too, had always assumed that Lavos reached full maturity/readiness/whatever in 1999 and that was it. Until I found/had other ideas (like him waiting until the last safe moment to annihilate the world).
I never bought into the "guided evolution" thing though. If he could do that, why go through the tens of millions of years of trouble? If he can guide evolution, just cut to the chase and figure out what DNA you want to be sequenced and be done with it. And! how did humans like Ayla already exist if he was so essential in guiding things? Nah, doesn't make sense. Marle's words when confronting him are misinterpreted a lot, I think.
So, I still like him observing, collecting, feeding off of... then killing everything for whichever reason and his generation moving on.