[neilm]

Each house number (known by the census taker) has only one answer except 31....

Thus needing further information implies the solution is either 15-15-1 or 25-3-3...

I say that only a potatohead would ask a 25 year old if they were the eldest in a house with a 25 year old and two three year olds, so it must be 15-15-1....