So instead of 1348-50 we are talking about 1375'ish?
First effects would be in the number of deaths, with an extra 25 years of growth the European population would be much larger (assuming average harvests, no major wars etc.).
Also a feudal system would remain intact for longer, another generation of nobility sponging off the sweat of the peasants.
England would not loose much of France in the Hundred Years War, and would be in a much stronger position to actually unite the thrones of France and England.