Submitting oldest living parent assignment.

It makes an object containing all the parents as keys, and then uses that object to filter the people array down to just the parents, where it then picks out the highest age by comparing the ages to the saved highest age (so far). 
1) The object made it easy to create just one entry per unique parent. One of my earlier solutions used a loop within a loop to identify parents, and that put Don into the "living parents" array three times, since he is the parent of three other people. (Checking if he was already in that array would have been yet another loop.)
2) The second for each loop can just grab the person directly by key, no need to check each index of an array.
3) Maybe other reasons? It definitely uses fewer lines.

This wasn't easy, I think I wrote this assignment at least 2 other ways (with nested loops) before arriving at this solution. This solution was inspired by the in-class example by Tyler, where he used an object to hold letters in an algorithm that looks for duplicate letters in a string.