Hi there
personally i'd think about sending your boy off if he's big enough at 24wks old, if you leave him with the girls longer than this he will definetly mate with them. We split all our boys & girl pigs up at 16wks as a precaution though we once kept a girl with 2 boys upto 22wks which is when they all went to the butcher. I have a 20wk old girl who has come into season already so they do mature early and sexual activity in boys is the biggest cause of boar taint. Is it possible for you to put him in a separate area next to the girls so he won't be lonely but can see them thro the fence until he goes off for pork?
HTH
mandy