Where there was no age given, the magus obviously could not appear in the age distribution. I reckon that no guesswork went into the stats, but for the 5 Spring magi per Tribunal clearly spelled out for the second distribution.
It is simple to add more Spring magi to taste: 5 more magi per Tribunal sifted through (Rhine, Normandy, Theban, Transsylvanian and Hibernian) make 25 total.
Another 15 - for a total of 20 - Spring magi added per Tribunal would be the minimum to get a population distribution sustainable under placid conditions: that is, magi under 71 passing into Final Twilight or dying only in exceptional cases.
Spring (Gauntlet – 35 years out of Gauntlet) 38%
Summer (36 – 70 years out of Gauntlet) 35.7%
Autumn (71 – 120 years out of Gauntlet) 24.7%
Winter (121 – 180 years out of Gauntlet) 6.4%
Deep Winter (181+ years out of Gauntlet) 0.28%
The simple fact is that spring magi are less likely to be signifigant and therefore less likely to be documented. It isn't as though this was a random sampling...
Do we have an example anywhere of winter or deep winter magi with full write ups? Even for the stuff I've done on this board I've not yet gone more than 120 years out of apprenticeship.
TtA's Winter covenant Longmist has full write-ups for Lugh-éccnaid of The Younger House (125 years) on p.105f and Conchobor Crosach of House Merinita (112 years) on p.106f.
TtA's Autumn covenant Didyma has a full write-up of its Patriarch Alexander of House Ex Miscellanea (129 years) on p.75f.
Just a few more years of your write-ups, and you beat these!
Dama of Merinita (193 years) on F&F p.70f is harder to reach, but is a very special being like the later Quendalon.
First of all, thank you all for your interventions! I went on vacation two weeks, and what a surprise to see this subject was lengthened by three pages of advice, all more relevant than the others!
I take note of the suggested supplements but it is a little constraining for me to recover books that have not been translated into French. (Alas ! The French range of Ars Magica books is very limited)
The Mages of the Order of Hermes do not play a political role (or at least are not supposed to be part of the feudal hierarchy), which distinguishes them from European chivalry.
Moreover, with rare exceptions, they probably avoid being parish priests or having an official office in the Church (if only because of Dominion auras).
In general, from what I read here, one can consider that the chances of finding a child who has the Gift vary around 1/49000 or 1/10000 depending on the pessimistic or optimistic estimates.
I am not convinced that being born a noble greatly increases the chances of reaching 6 years (and therefore the first signs of manifestation of the Gift). So I do not think that taking into account the social origin of children cound influence statistics.
There are, IMHO, only the children of the Magi who are more likely than others not to die quickly of disease (it is still necessary to give them the benefit of healing or proper hygiene spells, which may not be the case everywhere).
In any case, I do not think that we can consider them as part of the historical statistics of the clergy or the nobility.
It should be possible to determine if a child has the Gift, before she manifests it by herself, right? An Intellego spell should suffice ? (Unless the Gift really only invests human beings after a certain age ?)
In the absence of an appropriate Intellego spell, could the birth horoscope indicate whether a person has the Gift?
And if it were necessary to make a list of the factors that may be involved in the Don's event, the list would give something like:
-Local supernatural aura -other than Dominion though (from conception to birth, even in the first 5 years?)
-Gifted parents
-Parents with supernatural virtues
-Supernatural virtues granted to the child (Interest of supernatural beings to the child, demonic past, blessing of a fairy ...)
Temporary or permanent magical effects affecting the mother (before birth) and / or the child (after birth until age 5)
Do you have any other suggestions of determining factors?
A noble's child is much more likely to have access to a physician, who can help the child through childhood diseases. So yes, being nobly-born helps a lot.
Short form: Possibly but it takes seasons of work drawing up the appropriate inceptions. The rules for it are on A&A 72.
Also, a noble child will normally have better access to nutrition (including prenatal nutrition). Also, better living conditions in terms of being warm and dry, etc. Both of which will make a huge difference to survival rates (although not guarantee survival, of course).