Specialized ribosomes help determine which proteins are synthesized, however, the influence of age on ribosome heterogeneity and whether dysregulation of this process drives organismal aging is unknown. Here we examined the role of ribosomal RNA (rRNA) methylation in maintaining appropriate translation as organisms age. In a directed RNAi screen, we identified 18S rRNA N6'-dimethyl adenosine (mA) methyltransferase, dimt-1, as a regulator of C. elegans lifespan and stress resistance. We demonstrate that DIMT-1 functions in the germline after mid-life to regulate lifespan. Depletion of dimt-1 leads to selective translation of transcripts important for stress resistance and lifespan regulation in the C. elegans germline including the cytochrome P450 daf-9, which synthesizes a steroid that signals from the germline to the soma. dimt-1 induced lifespan extension is dependent on the daf-9 signaling pathway. Our findings highlight ribosome heterogeneity, and specific rRNA modifications, in maintaining appropriate translation later in life to promote healthy aging.