Three Questions abt Treasure Island

#1: When is it set?
JimH is famously coy (“I take up my pen in the year of grace 17__” only gives a clue abt when he WROTE it) but there are clues.
i. The King is a George = hence must be after 1716.
ii. Dr Livesey says he fought (and was wounded) at Fontenoy = hence must be after 1745.
iii. L. J. Silver tells Squire Trelawney that he lost his leg fighting under Hawke, and later mentions (to Jim) to “Admiral Hawke” = British naval hero Rear Admiral Edward Hawke, MP for Bristol, became a full-blown Admiral in the 1750s, hence… er, no. We encounter a morass of reliabilities. Is yarnspinner pirate and villain Silver a reliable teller of his own lifestory? We can assume JimH is NOT an unreliable narrator, but is he an accurate historian? Is Stevenson?
iv. Silver tells JimH that he began life as a sailor at Jim’s age, and that his parrot, Captain Flint, is a. 200 years old and b. sailed with the “great Cap’n England, the pirate”. Edward England – a legendary actual real historical pirate – was marooned on Mauritius and died a beggar in 1720.
v. Silver tells a raw pirate recruit that he himself sailed with England and Flint (ie the pirate the parrot is named for), and also that he (Silver) is a leader worth following bcz he has reached the age of 50 (to make this point he is more likely to exaggerate his age UP not down). Also the ship’s surgeon who amputated his leg was hanged at Corso Castle as a member of Captain Roberts’s crew. This would be the even more legendary Bartholomew ‘Black Bart‘ Roberts, who died in action in 1722.
vi. Ben Gunn, a shipmate of Silver’s under Flint, had been marooned (by the crew of another ship entirely ) for three years.

Assume for the sake of argument that Silver is 50 in 1756 => he would have been 14 the year England died, ie a cabinboy as claimed. But this would mean (assuming the surgeon-under-Roberts story is true) that he lost his leg before he was 16: surely too early for him to go on to establish himself as a physically courageous mega-seadog feared even by Flint (who is fictional btw) (and hired him pegleg and all).

My solution: the story takes place in the 1750s, but not later than 1758. Until 1755, Hawke was still only Rear Admiral but (since he had gone on being a naval hero and public figure in the interim) JimH misremembered exactly what Silver said. Silver only mentions England and Flint to the young pirate, so these really were his only pirate journeys. Service under Flint could surely not have lasted from the 1720s to the 1740s (for obvious reasons, the legendary pirate careers rarely lasted as long as a decade: Roberts’s was barely three years). Silver is 50 (or slightly less) at time of story and did sail with England as a young man – or possibly a cabin boy as young as 10, but the younger he was, the more certain it is that the story abt the surgeon is a yarn to impress the raw young pirate recruit. If Silver lost his leg later, in circs unknown, it was in non-piratical service – unlikely to have with Hawke, but not chronologically impossible, as the latter was at sea in the early 1740s. If pegleg Silver sailed under Flint, can Flint still have been active (as in burying treasure and singlehandedly killing the six pirates who buried it with him) as late as the late 40s? Given that he then has to have time to down and die of rum-bibbing in Savannah, while B.Gunn has to have time to be marooned?