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I think you can still upvote posts that are older than seven days old, so I don't see why it wouldn't let you vote for a comment even though it won't pay out. I'm probably wrong, though, I still don't quite understand how everything works here, haha.

Have you tried upvoting something older than 7 days? I haven't in a while, but I think it gave me an error message. Haha I don't quite remember.

I think when I first started I upvoted an older post, but I can't remember.

I think it does not earn anything after 7 days. I was thinking about a way around that. If I'd leave a comment on the "old post" and the author responds to that, the comment itself CAN still earn since it would be younger than 7 days. So people who re-discover the author could sill support them!