If we ignore for a moment that he’s 30, it seems somewhat reasonable to ask her parents when she’s 18, whereas asking her parents when she’s 30 seems weird.
Now, a 30 year old man asking the parents of an 18 year old woman is weirder than a 30 year old man asking the parents of a 30 year old woman, but not because asking the parents in that situation is weird, but because he’s 30 and she’s 18.