Teething question???

My neighbor has an 8mth old baby boy but she's worried because he still doesn't have any teeth so she just phoned me to see if I knew anything but I told her I wasn't to sure because two of mine started teething at 4mths and the other two started at 6mths so I was trying to get some info to give back to her because this is her first baby and she is not to sure on when the teeth come in the only thing I told her is that when the teeth are ready to come in they will