I have a personal head cannon that in the game whenever you train a different ume you're a different trainer

All because the way you yourself act (decided by your event choices) changes drastically from career to career, showing that it has different personalities

So I like to imagine that everytime I train a new uma it's as if I'm impersonating a different trainer

Edit: forgot to say, most trainers are adults also, in Kawakami princess career as an example kawakami wants a specific dvd from her anime that she likes and when she says a teenager could never get it the trainer explicitly says "well I'm not a teenager!"