system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] The mystery of the Heir of Slytherin.

Spoilers...

In Harry Potter and the Chamber of Secrets a monster is unleashed at Hogwarts because the Heir of Slytherin has RETURNED.

To me it would seem that the heir would, to have made the beast active simply by their return(at least to the eyes of the trio), be a first year student or even a new faculty member. 

So why/how could Harry and Malfoy be considered the Heir if it was their second year at Hogwarts and no one was petrified and there was no sign/activity involving the chamber of secrets/a basilisk during their entire first year?
gpt
There are a lot of reasons not to make that assumption. For example the heir may have needed to find the chamber then prove their cleverness to open it and claim their inheritance, that could have taken years. Next there is the idea that it was voldemort that passed down the knowledge, they knew he was active so he may have told anyone associated with the death eaters who could have passed it down to their children.