I agree with the 150 people answer, but I wanted to point out an additional fact:
Living longer doesn't help your character know more people, unless those other people are also long-lived.
The character will have known more people over the course of their lifetime, but most of those people will be dead by the time of your story. The number of people you "...
Roughly zero, unless there were other 3000-year-olds with similar outlook, interests and values.
Young people get increasingly irritating as grumpy old man syndrome strikes.
I mean, would they even speak the same language as anyone else alive?
To clarify — the terms of the question may have changed since I read it, but language changes and people would ...
I Agree with @Mathew Wells Answer, about 150 People. The question isn't about how long a person has lived it is about memory. People tend forget people, it starts with names, and eventually faces.
The statement average American knows about 600 people, or H. Russell Bernard and Peter Killworth, estimated from an earlier survey that the average American knew ...
As per the work of Robin Dunbar, 150 people seems to be the maximum number of acquaintances you can maintain without forgetting important details, and it'd be pretty dull having to deal with forgetting someone's birthday the 200th time, so I'd say people would probably organize into 100-150 person groups.