Fisetin is not a peptide. It is a flavonoid, a plant compound found in strawberries, apples and onions, and it is one of the more credible senolytic candidates. Senolytics work by selectively killing senescent cells, damaged cells that stop dividing but do not die, instead lingering in tissue and releasing inflammatory signals that appear to drive much of what we experience as ageing. In animal studies fisetin cleared these cells and extended lifespan. What distinguishes it from most things in this database is that the human trials are actually happening, run by the Mayo Clinic and others, several of them registered and ongoing. Results are largely still pending, which is a more honest position than almost anything else here.