We know that Hagrid is around the same age as Voldemort. I figure Hagrid is pretty old- must be in his 60's. In book 2- The COS was opened "50 years ago" and Hagrid was accused of setting the creature on the students. So we know that he knew Voldemort, cause that is basically who got him expelled.
He must have known James and Lily and that whole gang after he was groundskeeper- Because there is no way that James and Lily would have been in there 40's or 50's when Harry was born. It just wouldn't make sense.
Also, I'm re-reading GOF and this is something that baffled me:
Mr. and Mrs. Weasley are obviously older than James and Lily would be, because they have much older children and all that- but they must still be younger than Hagrid cause I also don't see them being that old. BUT, before the last task of the tri-wizard tournament, Harry takes Mrs. W and Bill on a tour of Hogwarts, and it mentions that she remenices (sp?) about the groundskeeper before Hagrid.... So that kinda confused me. Wouldn't she and Mr. W have been at school sometime AFTER Hagrid was made groundskeeper?
I may be thinking WAY too much into that, but if someone has an explanation, I'd love to hear it.
P.S. Sorry for hijacking the HBP discussion thread.