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.
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.