This sure looks like a modded game to me. Either that or he made a map made entirely of flooplains with wheat. He has an extremely large population and also has an extreme excess of food. I loaded up my Regent HoF game and I had a life expectancy of 72, and 1 child per family (I was maxed out in population, but I had 511 cities, so each city was about a size 12-14, and I hardly had any excess food anywhere).
Then I loaded up that game where I dogpiled 9600+ people in one city. I had a life expectancy of 90 and 3 children per family (the 3 children was because of all the other cities that had excess food and were currently building workers to add to that 'dog-pile capital'). Then I donated every city except the dogpile city to Cleo. My life expectancy shot up to 99, but children per family dropped to 1.
So it looks to me that 1 and 99 are hard coded limits. Life expectancy is related to your average city size, and children per family is how much excess food you have/city.