If old man Zhi was born during the Lost Generation, it meant that he stepped into the world near the end of the Sixth War of the Titans. If so, that would make him at least 300 years old!
However, the humans in RML, even those at the legendary realm, were not long-lived. At most, a human who enters the legendary realm should be able to live 150 years. Beyond that, it would require an extraordinary method to deny the hands of time. But, Izroth was not too surprised by this as such means were definitely attainable for someone at Zhi's level.
More importantly, according to Aurie, the Lost Generation was an era with a damaged Divinity Line. If so, how did someone like Zhi manage to become so powerful under such harsh restrictions? At the very least, Izroth could see why Aurie said he was born into the wrong era. If someone like that had been born during a period of time where the Divinity Line was normal, who knew how much more remarkable his accomplishments would be?