There are probably 'generic' Umamusume who may be well accomplished in-universe but age and die like humans while those that are isekaied from RL horses are timeless and ageless outside of re-enacting their other world counterpart's life.
Tracen Academy, my old alma mater... it's still the same as back then. How nostalgic.
Sempai didn't change either...
And neither did the chairwoman...
And her cat too...
So that time travel theory about Tracen was really true...