Some fans wonder how old Venti and Zhongli are in Genshin Impact.
Genshin Impact, like a lot of other gacha games, is deliberately vague in terms of telling the player how old the characters are. In TV Tropes, this is referred to as "Vague Age," which is often done not out of sheer laziness, but rather for marketing purposes in a game like Genshin Impact. If a player doesn't know how old the characters are, then they might be able to relate to them.
Of course, players can still guess how old some characters are. More than likely, there are some hints to a character's true age (particularly a range of how old they could be). China's drinking age is 18, so a lot of assumptions are made regarding that info for other characters. Fortunately, both Zhongli and Venti have more relevant info thanks to the revelation that they are Morax and Barbatos, respectively.
How old are Venti and Zhongli in Genshin Impact?
For all intents and purposes, the age of these characters will be identified as how much time has passed for their true selves. As Venti is Barbatos and Zhongli is Morax, it only makes sense to talk about their true ages as gods and not the biological age they take on.
Venti's age in Genshin Impact
Venti's age is never a specific number, but players do know that he is over 2600 years old. Back then, he was a nobody that befriended the Nameless Bard, of which they would eventually revolt against Decarabrian, the God of Storms.
Eventually, Barbatos would become the god he's worshipped as today and would create a vassal resembling the Nameless Bard. Naturally, Venti is allowed to drink, but sometimes, citizens of Mondstadt are put off by how young he looks. Still, Venti is the second oldest playable character in Genshin Impact.
Zhongli's age in Genshin Impact
Like Venti, Zhongli's true age is never specified. It's said that Morax is over 6000 years old, as he helped shape the geography of Liyue. Over 6000 years old is a vague number, but it confirms that Zhongli isn't anywhere below 6000 years. Predictably, this makes Zhongli the oldest character in Genshin Impact.
As for when Zhongli in his human form first showed up, that's unknown. It's likely that Morax had several human forms throughout the year, and that Zhongli is the current one the player sees.