When talking about children age * IQ / 100 ~= mental if it's under 16 works as a reasonable approximation for younger children across much of the IQ spectrum. So a 10 year old with an IQ of 70 has a mental age of 7, and someone with an IQ of 150 has a mental age of 15 etc. Now we have redefined IQ to have a more mathematical basis but the approximation still holds.
PS: It's not really completely accurate, but you can treat a 6 year old and a 12 year old with the same mental age in about the same way and see similar types of responses.
PS: It's not really completely accurate, but you can treat a 6 year old and a 12 year old with the same mental age in about the same way and see similar types of responses.