Is Folate good for longevity?

Yes — the evidence for this is strong. Folate's best-established benefit is preventing neural tube defects: a Cochrane review and multiple systematic reviews consistently support periconceptional folic acid supplementation for this purpose, one of the more unambiguous wins in preventive nutrition. That's reflected in an evidence score of 77/100 for its role in overall longevity, drawn from 9 studies, with an estimated impact on longevity rated moderate (60/100).