OK...after messing around with it, for a bit, it is as follows:
Townhall>Master Controller>Sim>Intermediate>Age Relative>Homeworld (Select your homeworld, you'll have to do it for each world if you want to keep everything in synch)>All
That will give you the Age in Days that you want to add to the entirety of the Sims of your homeworld. Now keep in mind that sometimes it will prompt you, other times it won't and it will select a Sim at random for you to add the age to...but since you have selected ALL it will apply the ages to ALL of them.
