This is what I think the dragon life cycle would be:
When the dragon hatches from its egg and stays with its mother and father in there cave. They will stay in the cave until the dragon is stage three. When it becomes stage three the dragon will dig out of the ground, now able to fend for itself. Its primary source of food are sheep, villagers, and humans. But it will go after anything smaller than it, including other smaller fire/ice dragons if its hungrey enough. When the dragon reaches stage 4 it will dig underground and create a dragon cave. It will then sit there until somthing comes into its cave in wich it will attept to tear the creature to shreds. When this happens the dragon will probably bust out of the cave and rein terror on the overworld until either somthing else kills it or it dies from old age. BUT if a dragon is female it will not come out of its cave. The reason is because when it becomes stage 4 it lays an egg (Makes sence because even if its a day over stage four it drop an egg when killed right) It will gaurd the egg. When the egg hatches it will continue to gaurd its young until they are stage three. It will then stay in the cave laying eggs and gaurding its young until it dies.
Most of the things I said are not in the mod. This stuff is just what I think would happen if the fire/ice dragon was real.