I didn't think it was bullying either, the biting never occurs unless the older one is mounting. In fact, the younger one tends to push the older one around more often. They are quite the pair.
We have two cherry head tortoises. The older one is approximately 5 years old, and younger one that is about 3 years old.
We always thought that the older one was female based on body shape, although (s)he has always demonstrated male-like behaviours such as head bobbing against the little...