Staghounds and virtually any dog with a lot of deerhound blood mature a lot more slowly than your standard pig dog Jake. Their bodies grow quickly, but it takes a long time for their minds to catch up.
Because they're so placid you can ruin them if you start them too early - that placid nature needs to be protected while they're young, so that it makes them calm, confident and steady when they're older. 18 months seems to be the minimum for a pure deerhound, some of the blokes start their stags at 12 months.
If you want him for pigs, my advice would be to let him run with the other d