I have just bonded to boars Sparky whose eight months and Tommie whose 9 weeks and it was so strange, I took Tommie over to a rescue in Cumbria and Graham (a member on here O0) put Tommie in a large run and introduced, one at a time another guinea pig to Tommie the first three where babies and Tommie completely freaked out and ran from each yet when he introduced the older boar he completley melted, settled right down and stared stuffing his face.
Since getting them home they have got on like a house on fire I just hope it continues, my concern is that when Tommie gets a bit older there could be a bust up as he decides he wants dominence. They have a large Nero three cage and seperate bowls, water bottle and houses but, they are quite content at the minute sharing a house!