Weaners at 8 weeks will use the protein in their diet a lot more efficiently than finishers at 24 weeks. There is, however, a limit to how much a pig can grow in a week and any excess is laid down as fat. If they're in a small enclosure with little to do except wait for the next feed time they won't need to build as much muscle as pigs with plenty of room and reason to explore and play so, again, will tend to lay down fat. Our GOS boar finishers are generally ready to go at 24 weeks but if I can't fit in a trip to the abattoir then I throttle back on feed, but still take them in at 26 weeks maximum.