That’s interesting how Obi-Wan was intended to be older. It sort of reminds me of Aragorn. Ewan McGregor did a good job in the role, but it was an odd choice for George to cast someone so young.
I don’t know how closely Lucas and Alan Dean Foster (who Ghost Wrote the novelisation) worked together. The novel was based on the second last screenplay draft, if memory serves. So we can never be sure of Obi-wans intended age on Day 1 of shooting SW77 in '76. So the whole Luke being surprised that Obi-Wan was old enough to have fought in the Wars thing might have been gone by then. I know that it was often assumed Palpatine’s aging was accelerated due to his abuse of darkside powers. Stated specifically in some 90s EU if memory serves (Shadows of the Empire). So maybe using The Force “properly” extended your lifespan. LOTR was almost assuredly an influence on Star Wars, so the whole humans with an extended lifespan thing might have come from there. Please note there is no canon source that states “lightsiders” live longer than regular people.
I do wonder what George was picturing when he thought of the Clone Wars. I suppose he just came up with the name as a way of intriguing the audience with unseen backstory, giving us a sense of some crazy wars off in space back in the olden days of the Republic. And when the time came to write the prequels, he had to figure out what the term “Clone Wars” actually entailed. I doubt he intended back in the 70’s for the clones to be the army protecting the Republic. I do wonder, though, at what point he came up with the idea that the Clone Wars were orchestrated by the Emperor to gain power, since there’s nothing to suggest that in the OT. Maybe originally, the Clone Wars were just a series of conflicts unrelated to the rise of the Empire, which just happened to occur around the same time.
It is almost a certainty that The Clone Wars were originally envisioned as either a battle against clones or a battle between opposing forces in which both sides had their manpower based on cloned soldiers. The Heir to the Empire Trilogy, whose story was carefully monitored by Lucas himself (or so rumour has it), certainly portrays one or the other. The rapid accelerated rate of maturity of Clones (perhaps increasing as opposing sides became more desperate - an arms race of a sort) is stated as producing “clone madness”. So you had a third force of crazy clones just killing anything or everything they could. It was often assumed that The Mandalorians were allied in some way with whomever was opposing The Old Republic. Were they clones as well?
So it seems likely that Lucas did not intend for Clones to be solely Republic forces until, at the earliest, he began writing TPM in '94.