What is the oldest a villager can be to procreate. I have let my tribe "age" too far and fear I am going to lose them all. My youngest villager is 53. I've lost them haven't I?

In VV3, the women stop having babies age 50 (the men can do it until they die, but if you don't have a woman under 50 that doesn't matter anyway).

.....but there are island events that can bring more people to the village, and I have seen one that makes a woman have a baby (and when it happened to me, the girl was only 14 so I don't think that event is governed by age!)

Maybe you'll get lucky with the events!

I think you've lost them when a villager reaches that age I don't think you can populate again.

There are events which bring new villagers - the best known is the barrel o' babies. I recommend starting a new village, and checking in every 24 hours (You have to check in each day to get the maximum number of events, and maximum chances at more babies) to check for events that might help you repopulate.

Additionally, if you want to use an exploit -- which is almost a cheat -- you can back up your save-game files. After doing that, load your game, and if the event isn't to your liking, quit, restore the files, and load again, until you get your barrel.