I'm always a bit shaky with this idea that the ages of Middle-earth can correspond to our own. Mostly as 'ages' must be incredibly short in the modern age! If an age must be thousands of years in length then shouldn't those early Elves and Men have been living in caves and having a hunter-gatherer existence? Oh wait, is that what Menegroth was all about?
Anyway, if we're having a bit of fun speculating, I'll stick me concerns on one side and join in. I'd say the 7th Age began around the time of the Boer War, the first significantly mechanised and 'modern' war, and the world has pretty much never been at peace since then. This broadly corresponds with the dawning of the modern secular age, the age of technological discovery, emancipation, globalisation, the beginning of the end of Empire, mass education etc.
6th age - Maybe the age of 'enlightenment' beginning around the late 1700s, which brought in new ideas on philosophy, the all-important Romantic movement, the expansion of discovery into the age of empire, the industrial revolution, American revolution, French revolution, and the shift from rural life to urban life.
5th age - The Middle ages and into the Reformation and the main era of global exploration.
4th age - The early middle ages (note, NOT Dark Ages) which would include the development of new cultures Norse/Saxon (AKA Rohirric) leading into the cataclysmic Norman Conquest (bah) - that could equate to the return of Sauron or something! Eek!