New family from Illinois

[Timberhillfarm]

We have a small herd of Nubians that we primarily use for milking and 4H. Our boys have gotten pretty attached to all our goats and a few of the bucklings have stayed on our farm. We have weathered a couple and he plans to train them to pull a cart. We have two bucklings we still need to wether and plan to train them to pack. All our goats wear collars and we have been walking them on a leash around our property. What age and what type of pack is recommended for training?