Gilts probably will be okay - depending on size and temprament, just keep an eye for bullys. My Berkshires and Large Blacks share quite happily(3 month age difference), as long as they've got plenty of room and fair share of the food

Mixing boars on the other hand is a definate no-no, they'll fight to the death. If you decide to go for seperate pens and have boars in each, block their view of each other and their ability to get nose to nose for the same reason.
HTH
Karen x