For now, we still do not have a complete understanding of any living cell.
The mycoplasmas have some of the simplest possible cells, so, as you suggest, they are good candidates for the first cells whose organization and functions will become completely known.
While it is unlikely that understanding a mycoplasma would provide direct information about the causes of senescence in any multicellular organism, there is no doubt that when either a mycoplasma or another of the simplest bacteria will become completely known, that will bring a huge jump in the knowledge about all living beings and from that moment on it will become much easier to discover the causes of senescence and how it might be prevented.
There are bacteria that have extraordinarily efficient mechanisms for DNA repair, so there is no doubt that it should be possible to improve the design of human cells to avoid the accumulation of genetic errors. However, this will not happen in a few years, but in at most a century from now it is very likely that this would be possible.
The mycoplasmas have some of the simplest possible cells, so, as you suggest, they are good candidates for the first cells whose organization and functions will become completely known.
While it is unlikely that understanding a mycoplasma would provide direct information about the causes of senescence in any multicellular organism, there is no doubt that when either a mycoplasma or another of the simplest bacteria will become completely known, that will bring a huge jump in the knowledge about all living beings and from that moment on it will become much easier to discover the causes of senescence and how it might be prevented.
There are bacteria that have extraordinarily efficient mechanisms for DNA repair, so there is no doubt that it should be possible to improve the design of human cells to avoid the accumulation of genetic errors. However, this will not happen in a few years, but in at most a century from now it is very likely that this would be possible.