Not sure if anyones doing anything wrong, but a callous is caused by friction and pressure. I would suspect those that run faster are more prone to them as they are exposed to greater forces and it's harder to maintain form at speed.
The road surfaces we run on could also be a factor.
I've got what i would call leathery skin in the places you mention, and at my age a lot more place i'd care not to mention.
I think it's in fact easier to maintain good form at higher velocities, as the body is forced to become as efficient as possible to conserve energy. Many endurance runners/trainers incorporate speed work for this very reason, to improve running economy.
Leathery skin is also a product of pressure and/or abrasion, so you're doing well, at any age, if you're callused in areas you'd care not to mention!
The problem with the barefooter's thick/leathery-skin-is-not-a-callus thesis is that we then have to posit two different physiological adaptations to different kinds of pressure and/or abrasion, rather than than just saying that it's the same physiological adaption, with different results depending on the degree or kind of pressure and/or abrasion. Sort of like how strength training and slouching in one's chair will lead to different adaptations/results, one good, one bad, even though they involve the same principles of neuro-muscular adaptation to habitual stimuli.
I've been a casual barefooter for quite some time, and I think it's perfectly normal if certain points on the plantar surface, such as the balls of feet, outer edge of the big toe, or heels, are a little thicker and more "callus-like" than other parts. It seems silly to think the pressure and/or abrasion of foot-landing will be evenly distributed, when the foot was in fact designed to 'roll' through the different phases of landing, shock absorption, elastic recoil and release or push-off (also known as one-legged forward hopping). If there are spots that are particularly abraded or blistering, then yes, that's a problem, but it's also something that will most probably be self-corrected via the wonderful proprioception afforded by barefoot walking/running.
Not looking for an argument, not claiming any special expertise, just putting in my two cents.