Kune Kune's are nice pigs anyway - castrated or not.
My 3 year old breeding boy is a big softy.
6 months isn't too old for castration at all - but if they're birth notified/registered and there's a
good potential breeding boar (must have 2 piri's to be eligable plus all the usual stuff) keeping one intact would be a good idea. If they're not registered and you're planning on eating them keep them intact, (providing taint isn't an issue for you) but seperate them from your gilts. They will be getting to the sexually mature stage now (if not already) and you don't want a piggy free for all orgy going on
The wee guy is so small compared to the others because he's been castrated early on - it does slow the growth. It doesn't affect personality so much - that's all to do with how you're treating and handling them
I have 2 boars from the same litter - 1 was castrated @ 6 weeks and the other @ 20 weeks, the first one to be castrated is teeny compared to his brother, but was the biggest pre-castration. Castrates are lovely to have around - they act as surrogate uncles for newly weaned litters and can be good company for a breeding boar when he's not with the ladies (again, I would only advise this with Kunes, can't comment on how it would work with other breeds) and let's face it, as adults they're fine on grass and very little hard feeding in the winter, so it's not a major drain on resources
HTH
Karen
PS I LOVE your piccies, very happy pigs - looking totally happy and having a rare old time in the sunshine