Board Thread:Questions and Answers/@comment-36674746-20180822101157/@comment-35973148-20180831134227

He's called an ancient beast, so he's potentially a few thousand years old, if not older. That's all I can say, really.

Age in the tower doesn't particularly matter to the residents, as aging isn't a constant thing as long as you wield Shinsoo. All that really seems to matter is how strong you are. Though, the older a ranker is the stronger they are, if Jinsung's words are to be believed.