This answer is intended to complement those of Denis de Bernardy and Luís Henrique
When compared over a similar time period, Danish, French and Leonese monarchs had shorter lives than their English counterparts who averaged 48.2 years (according to the data presented by Luís Henrique, calculated starting with Edward the Martyr to match the range of Denmark). The data here is from the List of Monarchs of Denmark, France and Leon plus various other Wikipedia pages.
From Sweyn I (b.960) to Christian I (d.1481) average 42.4 years (31 monarchs)
Note: This is excluding 4 monarchs whose dates of birth are unknown. Information on monarchs before 986 is too unreliable to be of much use.
The calculations for Danish medieval monarchs can be found here. At least 9 of the 31 on the list were killed or died from wounds in battle.
The Danish king who lived the longest was Eric VII of Pomerania (died 1459, aged between 76 and 78. The youngest was Olaf II who died 'unexpectedly' at the age of 16 in 1387.
From Clovis I (b. circa 466) to Louis XI (d. 1483) average 40.4 years (64 monarchs)
This excludes the disputed reign of the English Lancastrian King Henry VI. Kings up to Louis VII (died 1180) were Kings of the Franks.
None of the French kings in this time period had particularly long lives but more than half (12 of them) passed the age of 50. John the Posthumous had the shortest life: born 6 months after his father Louis X died, John lived just 5 days.
An analysis of the average age at death of French kings by House shows a clear pattern.
- Merovingian (486 – 751) average 36 years (27 monarchs)
- Carolingian (751 – 987) average 41 years (16 monarchs)
- Capet (987 – 1328) average 44 years (15 monarchs)
- Valois (1328 – 1483) average 52 years (6 monarchs)
Note: Included in the Carolingians are two Robertian kings and one Bosonid king.
The calculations for French medieval monarchs can be found here.
Perhaps somewhat unexpectedly, the two oldest medieval monarchs of France were both Kings of the Franks and pre-900 AD: Charlemagne (aged 71, died in 814) and the Merovigian king Chlothar I (aged about 64, died in 561).
Although the Capetian monarchs averaged 3 more years than the Carolingian ones, infant mortality was the same for the 9th century Carolingians (45% before the age of 20) as it was for the 13th century Capetians.
COMPARING THE ENGLISH, DANISH, FRENCH AND LEONESE MONARCHIES
Only by reducing the time periods for England and France to match that of Denmark can we make a meaningful comparison between the three monarchies. I've also added Leonese monarchs. (Note: the data for England is taken from the link provided by Luís Henrique)
- Edward the Martyr [b.962] to Edward IV [d. 1483] 48.2 years
- Louis V [b.966] to Louis XI [d.1483] 45.3 years
- Ramiro III [b.961] to Henry IV [d.1474] 42.7 years
- Sweyn I [b.960] to Christian I [d.1481] 42.4 years
For the adult royal family of Wales and associated Marcher relations (earliest born was 1168, last to die was 1333), Sarah Woodbury has calculated a life expectancy of 48.7 for men and 43.6 for women (but she doesn't say what age she starts with for adults).
COMPARING MONARCHS WITH THE GENERAL POPULATION
As already noted elsewhere on this site (see the link provided by the OP), life expectancy for a boy reaching the age of 20 in the 13th century medieval Britain was around 45. If we compare this to monarchs who were alive during at least part of the 12th, 13th & 14th centuries (using only the 13th century gives too small a sample), we get the following averages (Note: the data for England is taken from the link provided by Luís Henrique):
- Henry I [d.1135] to Henry V [b.1386] 53.4 years (13 monarchs)
- Philip I [d.1108] to Charles VI [b.1368] 46.1 years (15 monarchs)
- Alfonso VI [d.1109] to Henry III [b. 1379] 45 years (14 monarchs)
- Eric I [d.1103] to Eric VII [b.1381/2] 44.3 years (21 monarchs)
Note: John I (France) and Olaf II (Denmark) were excluded as they did not reach the age of 20. Sancha (Leon, b.1191/2) was excluded as her date of death is uncertain.
Although the samples are smaller than one would like to be fully confident of the figures, one can tentatively conclude (for 13th century England at least, given the 8-year difference between monarchs and the general population), that being a monarch meant you lived longer despite the undoubtedly higher murder rate.
Jean-Pierre Deregnaucourt, in La mort au Moyen Age: les hommes et la mort à la fin du Moyen Age, states that the life expectancy data for 13th century England given in Russel's British Medieval Population (p. 186) is applicable to France and Europe in general (this is also stated in one of Woodbury's aricles). This gives 31 as the life expectancy at birth, so it does not seem unreasonable to assume that life expectancy at 20 (45 years) was not much different in France either. For the 14th century, though, he states that the Hundred Years War had a greater effect on mortality rates in France than in England.