To continue the analogy, a Dodge Challenger with a 50-shot of nitrous on it that gets used once a day is gonna still come out looking better at any milage/age than the same engine in a Promaster van because you can't drive around at 17k gross in a Challenger so the area under the abuse curve is way lower even if it peaks ever so slightly higher.
An office worker on meth-lite (or whatever you want to call it) is still accumulating less wear and tear than a laborer, something the human body is clearly capable of being for a lifetime if you're somewhat smart about it.
Adderall, caffeine, heck cocaine based stimulants, are probably all fine if you're not over-using the living crap out of them and stacking large amounts of them on top of other things that'll beat the body up over time.