If you were 4 and now you are 44 then you might be an integer variable. If sister is also a variable, we don’t know when she was allocated. She might also be an integer constant in which case she’s arguably immortal.

If your parents had another daughter in the meantime (or if your older brother became female), “my sister” would still be a valid reference, to a completely different person.

I suspect the tipping point here is when you can get around to employing someone to have good taste and imagination, and take a real interest in artisanship on your behalf.