Metformin has a bunch of undesirable side effects. I don't see an easy way to quantify the importance of those side effects, so I try to evaluate how likely it is that the benefits of metformin will apply to me.

The obvious way in which metformin might cure or prevent age-related diseases is by curing insulin resistance. Some educated-sounding people have been saying that insulin resistance contributes significantly to Western disease (aka diseases of civilization, including cardiovascular disease, diabetes, dementia, and some subset of cancer). Doctors have arguably been undertreating insulin resistance, because it doesn't produce immediate disease-like symptoms. Maybe if metformin were still patented, the patentholder would be pushing the FDA to get insulin resistance classified as a disease.

Insulin resistance seems to be non-existent in cultures that most resemble our pre-farming ancestors, so it sure looks like it's avoidable via lifestyle changes (the best guesses are diet (high fiber, whole foods), exercise, and sleep). That suggests it's possible, although maybe hard, to get the benefits attributed to metformin without the side effects.

I pay close attention to my insulin resistance, via blood tests, and have avoided metformin for now because it looks like my lifestyle is good enough that I have few insulin-related risks so far. If my A1C gets above 5.6, I'll think pretty carefully about getting metformin.

It might be that everyone should take it, but the case for people over 40 seems clearer based on my non-expert interpretation of what it does because of their much greater risk of heart failure.

I have convinced two U.S. doctors (my first left general practice) to give me a prescription. I explained that I wanted the drug to reduce the risk of heart disease and cancer. I also explained that since the drug was cheap I would not be asking my insurance to pay for it so my doctor would not have to justify the prescription to my insurance company. If you ask for a prescription know what dosage you want and look up the possible negative side effects so it seems to your doctor that you have done your homework on the drug. If you have some reason why you are at a high risk for diabetes (such as a close relative has it) mention this as the drug is used to prevent diabetes.

I (the author of the FAQ) now have a bit more of an optimistic conclusion; but yeah I wouldn't just take metformin if you are healthy. Fwiw what -I- personally do in terms of supplements is just https://labdoor.com/review/whc-unocardio-1000-vitamin-d-1000 . Idk how strong the Vitamin D effect is, but I don't get much sun in the UK anyway. I think for overall health calorie restriction / intermittent fasting is the best intervention. Perhaps there are other things one can do in addition, but I think most of the value in terms of overall health can be achieved with this one thing.