One has to be at least 35 (!) to be President of the United States for example. Although that minimum age is probably excessive by international standards, it is still shocking that an 18-year-old, again with no preparation whatsoever, can be regent just because he is the eldest son of the King (i.e, by a mere accident iof birth). And, on the intellectual capabilities of politicians, whether they are questionable or not, at least they were judged by the voters who made a decision to put those politicians in government, and are subject to the scrutiny of the press and the civil society at large. It is a completely different situation from a hereditary (and unconditional) right to reign then.
The bottom line is that hereditary succession of the head of state is so out of touch with modern concepts of government that it has only become acceptable in European countries by making the King (or the regent) de facto powerless, i.e., a rubber stamp. Yes, in theory, the King or the regent could veto a law, or dismiss the government on his own discretion, but we know that this is not going to happen and, if it did happen, except in the most extreme circumstances, it would probably trigger a surge in support for republicanism.
I know monarchists dislike what happened in Sweden in 1974, but honestly the Swedes were right to take away the symbolic powers of the King to sign laws or appoint the government, as it was a constitutional fiction that no longer had any practical meaning.
EDIT: I apologize for being blunt and I do not want to create a controversy, but keep in mind that, not being a citizen of a monarchy, my personal perspective may be obviously different from someone who lives in Denmark. I respect that you and other monarchists in Denmark or elsewhere might disagree.
The types of monarchies you are describing in an archaic and negative fashion are very much in these years.
I can without problem mention a string of elected (often several times) heads of states who either are absolute monarchs in anything but name, would very much like to be absolute monarchs , are working on becoming absolute monarchs or who would crown themselves kings in a heartbeat if they thought they could get away with it.
Dictators, wannabes or otherwise being de facto absolute monarchs.
Some of them are even hereditary: North Korea and Syria springs to mind.
Most of the countries that score top marks in regards to securing human rights, democracy, freedom of speech etc. oddly enough have a monarch as head of state, so perhaps monarchy - even when the regent happens to be only 18 - isn't that outdated?
As for being 35+ even to be elected. Well, I can't say that impress me the slightest bit, considering the selection of both elected politicians as well as candidates in a certain large country that shall remain unnamed, I have seen quite a lot of 15 years old who act and talk more mature than them.
And if the voters, for whatever reasons, vote for shall we say power-hungry politicians and that has happened many times, what extra stop gap is there? Who else might have the public and political gravitas to oppose such a politician?
There are a number of democracies right now that IMO are 1-3 general elections from going fascist.
The press you say. Ha! - Almost all the press in one of these countries is extremist and so is their coverage.
A free press is of limited value if a large segment of the voters don't care or worse choose to ignore different views or declare it to be "fake news."
You say monarchies are out of touch. An interesting observation as it is well known that the monarchs or Norway, Denmark, Spain, Belgium, Japan, the Netherlands, Britain are known to be very much in touch and to be extremely well informed about political trends.
So the point is: When choosing between a high school student signing laws to make them valid or a populist signing these laws, I know which one I feel more safe with.
Happy Posting! 
Nice....considering you have no idea as to how things went.
