If you wanted it more historical, Age I would include military, with Arquebusiers and Pikes amongst other Early Modern units. USA and Mexico would play as a Western Euro/Spanish civ up until Fortress/Industrial Age. Etc, etc
Not exactly. During the AOE-3 time period, wood was relatively scarce and in much higher demand, while the Industrial Age allowed for mineral extraction like never before.
There is actually a lot of activity in age 1, with treasure hunting, and herding. But yes, as I said, the game has 5 eras, but it is compressed into only 3.