Were Jean de La Fontaine and Isaac Newton alive at the same time?
Yes. Jean de La Fontaine and Isaac Newton were alive at the same time for 52 years, from 1642 to 1695.
Jean de La Fontaine was 21 when Isaac Newton was born.
Isaac Newton was 52 when Jean de La Fontaine died, aged 73.
Isaac Newton
English mathematician and physicist
Born 25 December 1642 (Julian calendar) · died 20 March 1727 (Julian calendar), aged 84