Policies often have costs today but benefits far into the future, especially climate change and environmental policies. A critical dimension in this trade-off is politicians’ age, which impacts their life expectancy, career concerns, and what education they receive. We study this trade-off in the case of Brazilian mayors and environmental outcomes, using close elections. We find that when a young politician is elected, there is a reduction in deforestation and greenhouse gas emissions without significant effects on municipal GDP. Our study of mechanisms suggests young mayors matter because they belong to a new cohort, not because of age per se.