

You could also simplify by saying that assuming neither of them are dead, at some point while he is 44 she will be 42. Whether or not she is actually his sister seems to be irrelevant, she was stated to be his sister, so regardless of biological data, it is being presented as a fact assumption.
The space stuff is not currently possible and can be disregarded as well.
Additionally, Lemmy would be a hostile place if you happened to be a conservative-leaning Linux user. I know quite a few, but they aren’t on Reddit either.