Your points are valid. However, I think it's important that we have standard frameworks for evaluating the impact of new interventions that aim to improve wellbeing (lifestyle changes, pills, neuromodulation)

The number of years a person has lived is a good metric but that means if we're trying something new now, we need to wait for X years before saying this has an effect. X in your example being someone reaching 120years.

We can't wait that long :)