I'm not against the idea of Civ Switching, I think it's a great system, but the Age System restricting the Civ's you can be feels wrong to me.
For those who like challenge runs or want to try out the concept of being decades back technologically, it would be nice if you allowed the option for players to stick as the same Civ in the next Age.
Maybe even add "Challenge" Legacy Path
"Complete Exploration Age as Maya"
"Complete Modern Age as Maya"
Maybe give the player some boon - so whether you choose a new Civ and gain new bonuses, or if you stay the same with a small bonus is a decision you have to weigh up - boiling down to how much of a challenge you want.