Before 1550, 30 percent of noble men died in battle. After 1550, it was less than 5 percent.

From Lifespans of the European Elite, 800–1800 by Neil Cummins.  From the abstract:  

I analyze the adult age at death of 115,650 European nobles from 800 to 1800. Longevity began increasing long before 1800 and the Industrial Revolution, with marked increases around 1400 and again around 1650. Declines in violent deaths from battle contributed to some of this increase, but the majority must reflect other changes in individual behavior. There are historic spatial contours to European elite mortality; Northwest Europe achieved greater adult lifespans than the rest of Europe even by 1000 AD.

He elaborates with four principle findings:

First, plague, which afflicted Europe 1348–1700, killed nobles at a much lower rate than it did the general population. Second there were significant declines in the proportion of male deaths from battle violence, mostly before 1550. I am able to estimate, from the timing of deaths within the year, the fraction of males who died violently in each epoch. Before 1550, 30 percent of noble men died in battle. After 1550, it was less than 5 percent.

Third finding there was a common upwards trend in the adult lifespan of nobles even before 1800. But this improvement was concentrated in two periods. Around 1400, and then again around 1650, there were relatively sudden upwards movements in longevity. In England and Wales, for example, the average age at death of noble adults increased from 48 for those born 800–1400, to 54 for 1400–1650, and then 56 for 1650–1800. This rise is independent of the fall in violent battle deaths. Finally, I find that there were regional differences in elite adult lifespan favoring Northwest Europe, that emerged around 1000 ad. While average lifespan in England in 1400 was 54, in Southern Europe, as well as in Central and Eastern Europe, it was only 50. The cause of this geographic “effect” is unknown.