[misp]

In my view, controlling for a variable X doesn't directly strenghten a causal claim, but allows to "rule out" another plausible explanation. In a way it shows that the observed effect is not accounted for, even if we take X into account, which means that it could be that the father's age influences filial geekiness. It could still be the case that another variable (that was not controlled for) accounts for the effect.