this is one of the problems with pigs and the large variety of breeds feeding and there environment
where does it say that at 6months the pig has to go to slaughter equally you don't have to keep it to 120kgs
they all grow at different speeds and at different times of the year summer they will put more weight on than winter
blonde lives in oz where it is hot and the pigs develop faster all factors have to be considered
the younger the pig the less saleable meat the older (up to 120kgs) the more meat and produced at less per kilo
from approx 60 kilos-120kilos the last 60 are put on the carcase quicker and cheaper
it all comes down to your preference