How old is too old (LJ-wise)?

Sometimes I don't read LJ for several days and can find myself going back nearly 200 messages on my friends page. That can be 3-4 days and I sometimes hesitate to comment on entries that old, feeling that it's no longer relevant or the person/conversation has moved on.
What do you, my friends, do and what would you have me do if I find an old entry of yours?
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ALSO, if the late reply is or seems to be a "Hey, this post struck me and I didn't know how to reply and I thought about it some more and pondered and came up with THIS" then I really like it. It shows an appreciation for what I'm writing that goes beyond the in one ear and out the other feel that a lot of social media has.