I believe that modern medicine has reduced more than infant mortality. In fact, he gives example in the second paragraph. Yet he concentrates on infant mortality and maximum human lifespan.
Maximum human lifespan may have remained roughly the same but I think there is a higher percentage of people reaching that maximum.
hundreds of times more credit is due to the non medical sciences. For exponential improvements in sanitation, home and workplace safety, affordable nutrition, and on and on and on,