Once that mental capacity is there for doing the
sharing problem, then it's likely that you can make
use of the same neural machinery in order to gossip
about who did what to whom. That is to say: It's not
entirely a free lunch. It was paid for by the natural
selection for the sharing problem, but once you've got
the circuitry for monitoring sharing, then you can use
it for other things.
In this creative-explosion period, sometimes called
"the Mind's Big Bang," for some skills, clearly earlier
is better. For languages, as in Joseph's situation, later
is much more difficult. So, you can imagine a scenario
for a sensitive period early in life where being
exposed works much better than it does otherwise.
For example, some individuals manage to solve the
syntax problem with something like case marking,
where there are different forms of the word for if the
person is an actor versus a recipient (he and him; she
and her), and now there are kids overhearing this
structured language at an age where they're more
impressionable - literally, kids can softwire for these
things, apparently, becoming much more capable.