Ive been asking myself this for a few years now. Some pwo's have as much as 500 or 600 mgs of caffeine per dose! That is a crazy amount.
I also have an essential tremor which I can be self conscious about especially if Im doing any kind of public speaking engagement. And stimulants- especially caffeine- increase the tremor noticeably. Aside from that, something is going to give sooner or later. Maybe not at 50 or 55 but surely if you're slamming 4 or 5 hundred milligrams of caffeine and then lifting heavy weights for a few hours, you'd think it would eventually result in a heart attack or stroke, if not kidney damage from elevated blood pressure.
Ive struggled a lot with stimulant use. Mostly caffeine but modafinil, dextroamphetamine, Adderall, DMHA, DMAA
And have used pre-workouts for 20 years- since my mid 30s.
The thing is stimulants really don't do much for me but it's more of a mental addiction than physical. Im always looking for the so-called "focus" but stimulants don't actually enhance focus.
I have found that some "nootropics" enhance creativity and increase energy as a result of heightened euphoria, and certain things like music, for example, sounds better and so I use certain nootropics in place of preworkouts and have cut back on my stimulant use... again. The best nootropic is phenibut in any of its various forms, baclofen and gabapentin (all gabaminergics) seem to provide the 'focus' that pre-workouts promise.
I plan on trying methelene blue. Ive read/heard that it has nootropic effects but isn't necessarily a stimulant and mostly has antioxidant properties but haven't tried it myself.