Suki has been doing this with us since she was about 5-6 months old. She loves it too! She is very good about staying close enough to the bike, but far enough away. It really wears her out!
One word of advice...teach them the word, "Stop!" when you are about to break. Suki almost flipped me over my handle bars a few times when I had to stop suddenly (car coming in opposite direction, she sees another animal, etc.).