Metformin is the pharmaceutical version of Berberine [1] You can get Berberine without a prescription. Metformin has been used in the US for about 40 years and Berberine in Asia for about 3000 years, initially used to treat gut infections.
A couple things to note if you take either of those is that they put a heavy load on the liver and also deplete vitamin B12. It may be worth keeping an eye on liver enzymes if using either. Hydration is also important. I should also add that if you start doing either to stay near a restroom for the first few weeks.
Metformin may delay the onset of some chronic metabolic diseases but it won't extend maximum lifespan and there are significant negative side effects. It's certainly not a fountain of youth. Proper diet and exercise can deliver most of the same benefits with no medical drawbacks.
A couple things to note if you take either of those is that they put a heavy load on the liver and also deplete vitamin B12. It may be worth keeping an eye on liver enzymes if using either. Hydration is also important. I should also add that if you start doing either to stay near a restroom for the first few weeks.
[1] - https://examine.com/supplements/berberine/