As I understand it, each Age advances at 1 point per turn to a max of 200 points. You can add +5 points from each of 4 Legacies. Barring other bonuses they have't mentioned yet, then, each Age will therefore be between 180 and 200 turns and then you go into the Crisis Period of 3 stages. I don't believe they've said how long those Crisis Stages will last in turns, but given that they will probably not be Happy Times, I'd bet they will be short: probably no more than 15 - 20 turns for the entire Crisis Period,
Frankly, in Civ VI 95% or more of my games were decided long before 200 turns - frequently by the 100th turn - so even 180 turns/Age sounds like plenty to me - always depending, of course, on how the turns play in the new game.
Yes, I get that many people like to do speed runs (notably content creators) and finish their games in sub 200 turns. For me, I like to take the time and smell the roses. I rarely finish in under 200 turns. In fact, I'm probably around 250-300 turns. (Maybe I'm a freak?)
Will have to see what all goes into shortening the ages through in game action when the real gameplay videos come out.
On the other hand 160X3 turns = 480 turns potentially for a total game and that to me seems too long. I am slow but not that slow.
Could be tricky to balance. Will be Interested in further clarification from the devs.