I am sorry for the necro, but I wanted to say that I've been working of this problem for while on and off as I have a game where all of the characters are young.
Despite the lack information, I have recently discovered where and how young characters are flagged and have created a prototype adjustment script and mechanic items that do both the ability score adjustments and starting age calculations and then override them.
One issue I have noticed (and also submitted a bug to HL about), is that the NPC classes- for which the Young starting option was created, are do not even have tagged with the proper Age item to allow for random calculations, I had to do an assign for each of them through a mechanic manually.
Also, even if you do set the age as young for the hero, you also have to set what age track you wish to use, as classes can only pick one and unlike races, dont have two seperate listings if the hero is a normal or young character. Therefore you must do a findchild[cHelpXXX].tagreplace to override the default for the class.
I am sure there is an easier way to do this, perhaps to check the class and tell HL to change all instances of X to Y. for tags, but that creates problems where it a class that uses one age track does not mean that all classes with that track will convert over to the same young random age track.
I know I'm being confusing, but thats okay... I do that alot, and I understand what I'm saying which is kinda what matters :P.
Anyways, Once I've gotten the kinks worked out I'll post it for playtest, though, I do intend to release this as part of a book I'm wanting to sell, so there may be future source conflicts
