Ages are periods of time with fairly rough edges. Ages are defined usually by the advancements in civilization. However, it is important to note that different countries progressed at different rates, and is why ages don't have exact starts and finishes.
An age is not equivalent to an era, which has an official start and end point.
The Building Age began about a century before Era 1 when independent structures were built (hence the name). These structures were very simple shelters which quickly became more complicated.
The iron age began soon after Jaffretti became the first 'nation'. At this time, basic smelting was developed, so people could make rock into iron tools; and later, weapons.
The Drevnic Age began around when Myshzuul gained independence. This age is the only one marked by a specific date: E2Y1729M4D16. On this day, every country in the world (including Myshzuul) had made Drevni their official language.
The Pre-Modern Age began very soon after Mykolviin's independence. It is classified by the industrial evolution that took place then. Steam power was common for the age and later on the electric light bulb, electric heating, and oil power production was all common place.This age is know for its advancements in technology. By the end of the age, during the war of the sea, warfare was similar to that of WW1 on Earth.
The Steam Age began around year 6000 and marked the decline of steam engines. During this age, electrical machinery took over, and eventually lead to computing, automation, and new medical feats.