Hi Brian,
We personally believe that boars are much calmer if allowed to stay with their girl the whole time. We run several mature boars here and they always have a sow with them. Now we may switch them around from time to time. For e.g. right now due to it being winter we have brought our really pregnant sows up to the pasture nearest the barn. So then we took the "just bred" ones down to the boars in the pastures so that they have each other to keep warm etc. (Once they are bred, we can move them wherever as we know who is already bred to who,) Pigs are herd animals, they really like company of the same kind.
NOW you also have to know your sow & boar. Although we have raised Hampshire gilts/sows here before we have never had a Hampshire boar so I have NO idea what their temperament is like. Our Large Black boars are sweethearts & are extremely good with the piglets. Some of the sows like to be by themselves when they farrow & also if the boar is stealing too much of the food that can be a possible problem. We can get around that due to us running multiple sows so can bring the nursing one out & put a non-nursing one in . OR we just feed her separately in the inner part of the barn & then let her back out to pasture when she is finished. There is always a way to make it work but a boar by himself will be more ornery & will want to break through fence etc.
Not sure about you, but we want boars around that we are not scared of & can walk up to, give them a scratch etc.
As you are looking for a young mature boar make sure you check him out really well & ask why they are selling him. You don't want to buy someone's problem! (Mistreated, aggressive etc)
Liz