headcanon: lowbloods are taller than highbloods
reasoning: if lowbloods have a shorter lifespan, that means they metabolize and wear out their telomeres (the part of dna strands that let them replicate and grow new cells without unraveling) faster; aka, its a survival mechanism to be the tallest/strongest lowblood to get the heck outta dodge (the trial caves) and take ur place in the caste hierarchy before ur too old to reproduce

also, higher bloods (bc theyre at the top of the food chain) spend more of their time ruling governments/serving said government as part of the aristocracy, something that requires less physical prowess than physically defending yourself daily from the beasts that feed on unfortunate trolls and/or their lususes. meaning everyone thats a highblood (except feferi, since she still has to feed glyobolgblybly) wouldnt have to be as tall and buff like we all know aradia to be ; )