Can you help me name this fallacy?

It reminds me of my parents' claim that I would understand when I was older. I think this was evidence that they were clear in their own mind but didn't know how to communicate their perspective in a way that I would understand - they just translated that into the idea that I was not capable (yet) of understanding.

This seems to be a similar appeal to authority without specifying the authority.

My parents were appealing to an authority that comes with age. In your example the authority is 'anyone who knows about that'.

The fallacious thinking is that everyone that falls into the category of 'old enough' or 'knows enough' will agree. This seems incredibly unlikely so maybe a useful question when faced with this would be, "How do you know that everyone who knows about that wouldn't come to that conclusion?" or even, "What do they know that makes this conclusion obviously wrong?"

It is probably just factually wrong. Overlooking the hyperbole, (i.e., "anyone") it might be the case that perhaps only 60% of people "who know about that" would come to a particular conclusion.

In argumentation, this could be poisoning the well assuming an audience is present. One can also argue amazing familiarity . How can anyone really know that?

"Anyone who knows about that wouldn't come to that conclusion - obviously"

I'm thinking this might be an example of proof surrogate. The language "anyone who knows" and "obviously" are filling the place of evidence for the claim being made.

The problem is that the responder is assuming that if you know about X, you won't reach conclusion Y (where no reason or evidence is given as to why X and Y are incompatible). 

It could also be begging the question.

Conclusion:  "Anyone who knows about that wouldn't come to that conclusion."

Reason: It's obvious.

We could say that the reason is another way or stating the conclusion. 

Exceptions:

Maybe a salesperson is claiming to be an expert on something to sell you something. But that person says something that anyone who knows about that wouldn't come to that conclusion. This sort of thinking might be a safeguard from making the wrong purchase.

Begging the question 

The argument uses the conclusion as a premise.

Jack " I believe crows are heavier than magpies"

Betty "You idiot ..... if you knew anything at all, you'd know that magpies are  heavier than crows"

Premise1 : Magpies are heavier than crows  / premise 2: None

Conclusion:   Magpies are heavier than crows  ..... I think the  "everyone knows this fact" not relevant to the error ..... just used as a 'vector' to pad out the circular argument ..... I mean, no one would dare say "fact X ... because fact X" ..... it has to be packaged in a vector of some sort to make it deliverable.

The Fallacy of the Argument from Intimidation appeals to moral self-doubt and reliance on the victim’s fear, guilt, or ignorance. It is used as an ultimatum demanding that the victim renounce a given idea without discussion, personally attacking by threatening the victim of being considered morally unworthy, uneducated, or just plain stupid. An ad hominem attack. In my experience, the pattern: “Only those who are evil (dishonest, heartless, insensitive, ignorant, etc.) can hold such an idea.” Or, “everyone knows that ...” 

 It is also the Fallacy of Diversion because it is a means of forestalling debate and bypassing logic by diverting the focus of the discussion to the victim.