AGI is probably not needed for this. Understanding and manipulating biological systems is a pretty specific problem for which narrow AI can be made. It's mainly about having a good model (which we largely have now but AI models are not general enough to represent them well yet), generating a hypothesis to explain an observation / disease state (the main use of the AI), testing the hypothesis (the hard part currently) and then updating the model with the new information.

Of course, if completely new chemistry needs to be invented to solve some of these problems, then the AI needs to be more general. I don't think that's the case with something like biological ageing though.