Technically they died at around 18 years old (that's not really a spoiler) and have lived for about 5(?) Year's as the reborn emperor's illegitimate twins. Though you can say they possess 25 years of memories, i feel that they still have the mindsets of teenagers because they never actually managed to get passed that actual age (though one may grow wiser with age, age does not make one wise ---- I'm not saying they're stupid, it's just that they died at 18 and basically had a restart for five years: they didn't technically learn anything 'new' in that time except adult abuse and some of the social rules of their new world, so I'd say they have an excuse for why they don't think entirely as fully mature adults at times
That's my 2 cents anyway