Just to bump this a bit. I have 4 of these "top of room" EX4500 virtual chassis switches. On 2 of them I can clearly see ages on some mac addresses, and they count down. There are many macs that have an age of 0. On the other 2 switches, all macs have an age of 0. The switch that isn't causing me a problem doesn't have misbehaving machines so it's mac table is reasonable.
I'm wondering why a mac address gets an age of 0 though. I'll have to study that.