Why do toenails seem to get thicker and tougher with age? Is there some evolutionary advantage for this aside of being more able to kick ass?
Thickening nails is a classic symptom of a fungal infection.
Damn, and here I was thinking I was gaining super ass kicking powers.
Toenails without fungal infection also seem thicker and tougher.
I did once ask (elsewhere) why toenails grew more slowly than fingernails and got the answer that it was all to do with blood flow. Is that a factor here?
Just wanted to note that “being more able to kick more ass” is one of the top evolutionary advantages that gets selected for. Possibly right after “attractive to the opposite sex.”
My ex married me because of my sexy, thick toenails. She left me for someone with thicker nails. 
Thickened nails are usually caused by fungal infection (onychomycosis), but there are other causes, like psoriatic nails, metabolic disorders as well as macro- or micro-trauma to the nail matrix (nail root).
I would guess that there hasn’t been much research on thickening nails related to aging, but that it’s related to the last factor here and general deterioration of the aging body.
You get older, your skin gets less elastic, your joints wear out and your nail matrix deteriorates and accumulates irreversible trauma.
My whole body is suffering from accumulated irreversible trauma. It’s noticably sagging southward and ending up at my toenails.
I just take one blue pill every day, and my doctor tells me I have the nails of a man half my age.
Hold it, your theory is gravitational tissue migration?
Try as I may, I can’t dispute this.
[gulf clapp]
Eat someTree of Life root, become a Pak Protector.