1) Not clear how lit review published in 2021 casts doubt on a study published in 2024
2) The lit review does not say the data is controversial, only that the claim of life extension is, and then goes on to say "However, via its ability to reduce early mortality associated with various diseases, including diabetes, cardiovascular disease, cognitive decline and cancer, metformin can improve healthspan thereby extending the period of life spent in good health" which is entirely consistent with the monkey study under discussion here
2) The lit review does not say the data is controversial, only that the claim of life extension is, and then goes on to say "However, via its ability to reduce early mortality associated with various diseases, including diabetes, cardiovascular disease, cognitive decline and cancer, metformin can improve healthspan thereby extending the period of life spent in good health" which is entirely consistent with the monkey study under discussion here