The flavonoid quercetin (Q) has recently been suggested as a natural anti-aging and senolytic agent. However, its low stability and poor oral bioavailability limit its benefits and practical application. To address this, a lecithin-based formulation called Quercefit™ Phytosome™ (QF) was developed, which can greatly enhance Q's absorption in humans. This study examines whether QF can improve Q's ability to delay aging and senescence in vivo using the nematode Caenorhabditis elegans. QF provided more effective protection for worms than Q against toxicity caused by thermal and oxidative stress, with effects similar to those of standard antioxidant compounds. Under thermal stress, QF, like Q, increased the worms' lifespan and health span by approximately 50%, counteracting the age-related decline associated with stress. These benefits are supported by QF's capacity to act as a reactive oxygen species scavenger, suppress heat-shock element gene transcription activated by thermal stress, such as hsp-16.2 and hsp-70, and stimulate sod-3 and gst-4 genes involved in antioxidant and detoxification responses. These findings suggest that QF can act at the transcriptional level, protecting against aging and senescence promoted by stressful conditions.