As Ebs and Fame already said, don't push through the ages too fast. You might give yourself an unnecessary handicap that way, if you're not prepared for the stronger opposition. This includes PVE and PVP, cause on average the players in your neighborhood will be stronger as well in the next age.
I always found the final stage 4 GE encounter a good indicator for what your absolute minimum strength should be in any given age.
On this page in the section "Enemy Defending Army Bonuses" check the percentage that's listed for Difficulty Level IV > Q4 > 64th. That's what you should at the very least aim for, unless you want to play as a pure negotiator. Which most players don't do, because that can get obscenely expensive with GE and especially GBG.