Intelligence isn't a full measure of knowledge, but then you knew that. You can have two equally intelligent people, and one can know much more than the other. Age is one of the main factors for knowledge.
That's real life. The game doesn't function that way. Within DnD, the Intelligence stat actually does measure your knowledge to a degree.
Also, age is one of the main factors, but having a high age and a low knowledge actually works against you in IQ tests, as you'll score lowly for your IQ if you have that combination.
Also, note the generally low Wisdom scores for something that old. In order for your argument to hold any water, those Wisdom scores would need to be higher (ignoring, as you are, what the game text shows of what the scores actually measure).
Age does translate into much greater knowledge, though.
Age is the
potential for having gained knowledge at some point. But just as being seventy years old doesn't automatically make someone in real life a computer expert, having a great age does not automatically mean a dragon in DnD will have more experience or knowledge than the party does.
And yet still won't have as much knowledge as the 50 year old professor who never left his home town.
For knowledge of the rest of the world? He might. It depends on what the professor teaches, how recent his education is, if he bothered to keep up on furthering education...
There's a massive number of factors involved in knowledge. Age is just a minor one.
By the time they are ancient, they've encountered, talked to, and beaten more adventurers than the party will face in it's entire existence. Even if they don't leave, people come to them, and they do leave. They plunder towns, caravans, and more.
Depends on the dragon. Even the MM notes that different species of dragons act differently, and that different members of the same species are not going to act the same. So, really, you're talking about a very specific dragon or very specific dragon personality and not even the majority of dragons.
As for the MM, here is what it says about chromatic dragons. Insulting one isn't going to do jack.
"Trying to humble a chromatic dragon is like trying to convince the wind to stop blowing. To these creatures, humanoids are animals, fit to serve as prey or beasts of burden, and wholly unworthy of respect."
You misunderstand the meaning of the word "humble." "Humble" is basically to actually reduce someone's worth. Not to imply that it is beneath you as an insult.
Here's what else it says about chromatics:
"Chromatic dragons lust after treasure, and this greed colors their every scheme and plot. They believe that the world's wealth belongs to them by right, and a chromatic dragon seizes that wealth without regard for the humanoids and other creatures that have "stolen" it."
"Chromatic dragons are united by their sense of superiority, believing themselves the most
powerful and worthy of all mortal creatures. When they interact with other creatures, it is only to further their
own interests. They believe in their innate right to rule, and this belief is the cornerstone of every chromatic dragon's personality and worldview."
So, basically, threaten its horde or suggest it is lesser than you, and you are insulting the creature in a way it has to respond.
Plus, take a look at this text from the red dragon entry:
"Red dragons fly into destructive rages and act on impulse when angered. They are so ferocious and vengeful that they are regarded as the archetypical evil dragon by many cultures."
So, in other words, dragons
can be angered, and some actually have quite short tempers and extremely poor impulse control when ticked off. All of that wisdom you talk about that comes with age? Here's proof it doesn't apply.
Here is what it says about metallic dragons.
"Metallic dragons covet treasure as do their evil chromatic kin, but they aren't driven as much by greed in their pursuit of wealth. Rather, metallic dragons are and collect, taking unclaimed relics and storing them in their lairs. A metallic dragon's treasure hoard is filled with items that reflect its persona, tell its history, and preserve its memories."
And.
"When a dragon learns how to disguise itself, it might immerse itself in other cultures for a time. Some dragons are too shy or paranoid to stray far from their lairs and their treasure hoards, but bolder dragons love to wander city streets in humanoid form, taking in the local culture and cuisine, and amusing themselves by observing how the smaller races live."
And.
"Metallic dragons have long memories, and they form opinions of humanoids based on previous contact with related humanoids. "
And here's more of what it says:
"Some metallic dragons prefer to s tay as far away from civilization as possible so as to not attract enemies. However, this means that they are often far out of touch with current events."
Remember what I said about long lives and inexperience?
"A gold dragon might never suspect duplicity from a cunning villain, assuming that the villain is of the same mind and heart as a good and virtuous grandmother. On the other hand, the dragon might resent a noble paladin whose ancestor stole a silver statue from the dragon's hoard three centuries before."
In other words, a gold dragon isn't really that wise as far as the differences between people across generations, but can actually be played as a total fool by someone with a virtuous ancestor who is evil.
Notice how it is that these texts make it clear that dragons are not all that wise once you stop removing the text that disagrees with your theory?