What was the significance of the boys' ages?What might these ages represent in society today and what do these ages say about teenagers in general?

The boys are divided up into 3 groups with regard to age -
the "big'uns" the "middle 'uns" and the "litle 'uns". The "big' uns" are at the most
pre-teens. None of the exact ages are given, but the oldest boys are probably middle
school aged boys. They are still interested in pretend play and have bouts of
semi-maturity, but none of them are older teens. They are just too immature. This is
significant because Golding wanted to show that even young children have, at their core,
an evil nature and that it is man's evil nature, that is inherent, that can do him in,
not the corrupting effects of society. The young boys are innocent children at the
beginning of the novel and this is significant because they need to be as far removed
from civilization age-wise as possible to still be
"innocent".

I am not sure what you mean about what this
says about teenagers today, since the oldest boys are most likely not
teenagers (they are 12-ish). I don't think this novel would work if the boys
were teens - they need to be as far away from adulthood as possible, yet still be old
enough to have some semblance of rationale because it is the older ones that get things
organized and the younger ones, when they are not crying, just go along and hope the
older boys will take care of them.