The vast majority of the population were slaves, who had to be well-muscled to lift heavy stones to build all those beaux-arts star forts of the Tartarian Empire. Then there were the barbarian warriors, who needed the musculature to effectively wield a zweihänder. If you saw a skinny dude, chances are he was an evil wizard.
It's basically ignoring at least 4,000 years of human civilization prior to that. The stone age is generally when people start talking about the origins of humans, despite us existing for a couple hundred thousand years prior to that.
I suppose I'm not conflating "rise" with "genesis". Human organizational structure was slow to ramp up and I don't think the bronze age is a terrible place to draw a line and say "this is where things start to heat up".
The biggest issue I see here is a man with clearly a great enough surplus of food to bulk. That wasn't happening unless you had access to a large farming community supporting you at the expense of most others and at least a rudimentary knowledge of nutrition.