> Young_behavior has significant clusters while Aged_behavior does not. Would this indicate then
> that young animals have increased connectivity between the seed and these positive clusters
> and that this connectivity is important for cognitive performance?

At least you have some strong evidence for the positive effect of cognitive performance at those regions for the young group.

> Does this say there is no relationship in aged animals and just young?

No, for two reasons: 1) no strong evidence of an effect is not the same as an evidence of no effect, and 2) you're assuming linearity for the effect of cognitive performance. For 1): if you set a threshold of voxel-wise p-value of 0.05 or even 0.1, do you see something meaningful? If you're willing to focus on a list of regions, a region-based approach may allow more exploratory analyses (e.g., nonlinear relationship).

Gang