Looks like you went past Mt Killimanjaro which gives a promotion that gives double movement on hills, which combined with the scouts ability to ignore difficult terrain means 4 moves on hills. I think it also grants faster healing or something.
Fountain of youth only heals. Pretty sure only Mt Kilimanjaro gives extra movement on hills.
I would figure that scouts from the Inca get the same benefits as any scout since all scouts ignore terrain modifiers to movement.
Speaking of which, can anyone tell me what happens to chariots with this promotion? Do they move four spaces through hills?
Altitude training promotion can be really useful, if it's close to me territory and I have hills around my cities I usually despatch all my troops to Killi for the training before returning home for deployment.
Never even seen the Fountain of Youth.