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Unless those aliens are close. There are a few stars within 5 light years, it seems reasonable that a sufficiently advanced civilization could reach us from that close in a reasonable amount of time. if they are really long lived 100 light years seems like the outside edge of reasonable travel distance.

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Why do you think 100 light years is the edge of "reasonable travel distance"? I put to you that you are imposing your human standards on other species, assuming that what seems to you to be a long time would also be a long time to another species.

Maybe the aliens have an average livespan of 200k Earth-years. Maybe much more. Maybe they experience time differently, and for them a 100 year journey feels to them like a walk around the block.

100 light years is arbitrary, but even for long lives things it seems like too far - few things on earth are that long lived, and bodies do break down over time, as do spaceships.

Until we know the entire universe (because of the way the universe is expanding this is impossible) we cannot do more than apply our best guess, but I think I hit a good upper limit. Even if I'm off I seems unlikely it is by much.

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