Cut the pound cake into 1-inch squares and set aside.
In a medium bowl add the strawberries and blackberries, and mix together. Pour the agave over the berries and gently mix. Set aside so the juices can start to mingle together, about 15 minutes.
In single-serving parfait dishes, layer some cake pieces, followed by some berries and then some of the whipped topping. Repeat the layers again: cake, then berries and then whipped topping. Drizzle with a little extra agave syrup or juice leftover from the berry mixture. Rest the parfaits for 20 minutes and then serve.