My youngest already has six (he's not quite eight months) and I'm pretty sure he's working on more right now. The last four pretty much came in all at once. The first two started coming in about 4 months.

The other two were completely different. When this one started cutting four, I called an dentist friend of mine. He said it wasn't usual to cut that many, but it wasn't abnormal or going to hurt him in the future.

Every one cuts teeth differently.