Is it just a coincidence that the two monarchs who were instrumental in the biggest upheavals of this country's lurches towards modernity weren't actually born to rule? I've no idea, but it is a fact that both Henry VIII and Charles I came into the world as Spares rather than Heirs Apparent, and only moved into pole position at the age of eleven, or thereabouts, the elder brothers both having died around the age of eighteen.
It's one of those pointless "what if" questions as to whether subsequent history would have proceeded any differently if that hadn't happened, not least because the elder brothers never had much chance to show what sort of king they might have been. current exhibition on Henry Frederick, Charles I's brother, tries to give an idea of what he was like, though how much is contemporary hagiography is hard to tell. He was (of course) a paragon of all the princely virtues of the time - one wonders if some of the praise heaped upon him was intended or seen as some sort of implied criticism of his father. He apparently had his own ideas about foreign policy (as least as regards potential marriages), and about Sir Walter Raleigh (not one of the king's favourite people). He assembled the basis of Charles I's famous art collections, and after his death poets and composers seem to have been more than perfunctorily productive in the lamentation department.
One thing is clear, though. If his death aroused seemingly mediaeval suspicions of poisoning, an emerging modern science made clear through an autopsy report (also part of the exhibition) that he was genuinely sick - with what seems to today's scientists to be typhoid fever. Unfortunately, science hadn't yet got as far as to do anything about the malevolence of Jacobean drains, for which no amount of princely virtues could be much of a match.