i wonder... why prime kept himself young? the concept could go well with his narcissism but if nothing doesn't matter in the end, why does he care?
loophole! I think he's not as detached as he would love us to believe. because, he cares about being superior, if he was so sure of himself he would consider himself superior either way, young or old.
also I think he likes being young, what a little diva, so obsessed with himself. gotta love him for that.