A "perfect sacrifice," well... it certainly is "God Mode" in a sense, though for a perfect sacrifice to happen there has to be a really big stroke of luck for Moctezuma. It's not something that would happen often, if at all. An "average" sacrifice would be like the random soldier Monty killed in battle a while back, a "good" sacrifice would be a regular man in Alexander's army or Genghis Khan's army, and a "great" sacrifice would be a powerful Heroic Spirit, like one of the generals themselves. A perfect sacrifice is more conditional, and requires not a strong soul to be given as an offering, but something a little different. You might see it, who knows.
And the Fountain of Youth pretty much just keeps you at the peak of your physical age forever. So, a fifty year old would become twenty-five or so again, but a fifteen year old would just stay young for an exceptionally long time and not age as much. Its main effect is geared towards older people, since it's the Fountain of Youth. It's a much higher-quality relic than even the potion of youth that Gilgamesh has, but it's likely that Gil has a giant, old Fountain of Youth prototype in his vault, but didn't use it because as a Heroic Spirit, it wouldn't really work on him. Only works on mortals and all.
His Charisma rank is A--. So, instead of being the usual 50 of A-rank, it's 50 divided in two twice, making it 25-25, equalling 0. In other words, he has no actual Charisma; this is a result of his people losing faith in him. However, since he has a ridiculously high Golden Rule skill level, he gets the condition that he can use his riches to influence people to follow him. Yet, since that's more of a persuasive thing and not based on actual charismatic presence, it's very fallible.I feel like I didn't quite understand how the bolded part works though, personally. Does that mean he can inspire people with his riches, but loses Charisma entirely if that fails? I'd probably stick with A rank Charisma than chance the + modifier. ^^;
^ You'll see why he's a Rider, and why his NP is EX-ranked. Oh, you will see, ahahahahaha!