This is impossible without knowing where YOU are relative to north already.
The only application this has is if you have an existing map, but do not know where you are on it. Cast your spell on two different people, or on a single grog that moves some measurable distance and the resulting triangle allows you to find yourself.
Completely unrelated to the topic at hand, but did I miss a post, or did you just predict JL's thoughts before he stated them?
I am that obvious. 
Hi,
Since location is an accidental property of something, why shouldn't InFo(other Forms of that thing) detect that property?
Anyway,
Ken
Yes, it is an accidental property, not an essential property of an object. IMO, Intellego can only determine essential properties of an object. An object isn't (in this case a person) isn't essentially north, it is north relative to some other objective measurement, that is unknowable from the underlying Form.
The right kind of spell could know if the object is well relative to the objective ideal of the Form.
What about InIm- which way do the shadows point?
By that reasoning, since time is an accidental property, InCo cannot tell you date of birth.
No, it can't. But it can tell you the age of the person in an objective fashion. The age, however, may not have anything to do with the date of birth in a world where regios with time dilation or acceleration exist.
What does "objective fashion" even mean? Someone with an actual age of 39 but an apparent age of 49 will show up as what? What about someone with Unaging? Or someone who has been magically aged 5 years?
If InCo reveals the actual age, then it is measuring actual time rather than effect of time on a body, and we are back to InCoing the accidental property of time except we are using a different word.
Anyway,
Ken
Actual age. Someone with unaging is still 39 if they appear to be 15 and are actually 39. If they have been magically aged 5 years, they will appear to be their age (since it has been increased by 5 years). What is actual age? Is it their time since date of birth, or some other measurable property?
All I'm saying is that InCo can give you a bearing to the person. Directions relative to some externally defined property isn't something that InCo should be able to detect. How does the body know that it is north? It is also an accidental property to know that a body is in a different location and bearing from another, but at least that property is relative to the caster and the target of the magic.
(tongue in cheek)
InVi- which way is the faerie region known as Santa's workshop?
-5 to Casting Total, for cheeked tongue garbling words 
"Sail north until you fall off the world." "You can't fall off the world, you'll just keep going back around..." "Exactly."
Where is the North is a hard one.
We not the only ones arguing about it. To this day, the North geographic pole is the southern magnetic pole...
I would say that you can make the question very interesting game wise. As mentioned above, plants, dirt, animals, etc. might be able to provide an answer but it might not always give the right answer. Trees might be sick or infested, birds might suffer from magnetic interference, but generally speaking, physical nature has the right answer. Then you could ask nature herself, or god, or a titan. You could conjure them (aside from god) and bid them to answer the debilitating question!
According to wiki, the use of a compass hit mythic europe around the start of the 13th century. Magi could be behind the idea or sailors that got it from asia... Imitating a compass probably requires a magnetic metal and a low InTe to know where it is drawn to. Paradigm probably dictates that without that piece of roch, it is probably an InAu to learn a property of something that is everywhere & nowhere.
An obsessed Mercere might send a delegation to the north pole to get a rock & have it fixed so that the could would hence then always know the north. They probably did come to think about it... & then a crazy magus inverses the two poles, thus confusing all
W
The body doesn't have to "know" anything. If it knew, it would be Mentem.
BTW, the rules you suggest above mean that you cannot reliably use InMe to figure out DoB.
I'm not saying that I agree with your version, btw.
considers If there hadn't been a guideline published, I would have ruled similarly to you but not exactly: InCo could determine the aging of a body but not necessarily the actual age. Someone with Unaging would show up as young right until the end; someone who makes 2 aging rolls/year would usually show up as older than chronology would indicate, and someone with the body of a 25 year old would be detected to have the body of a 25 year old, whether that body was actually 10 or 50.
I'm just saying it isn't a property of the body. And you are correct, the body doesn't know what is north because it doesn't matter to the body, it isn't internal to the body.
Well, you can use InMe to determine how old the person thinks they are. Which, for the right magus might be much easier than using InCo to determine actual age.
A person with Unaging still ages, they just don't show any outward signs of that age. They still gain decrepitude, but it doesn't impact their Characteristics. They are still 30 or 25 or 50 years old, no matter their apparent age.
MuTe to give a rock the properties of magnetic and floats on water... it doesn't use In, but it gets the job done.
InTe on any metal object "which way is the earth's magnetism pulling it"
The biggest problem with finding the faerie regio known as Santas workshop is that it will be several centuries before lore puts his workshop at the north pole...
of course keeping ACs on hand for suitably distant points and using InTe to determine the direction to them would work... if you know the direction to Cairo, Jerusalem, Stonehenge, and the Rock of Gibraltar (pillars of Hercules) it becomes pretty easy to figure out north...
Indeed, I am correct! 
But the body doesn't know what is north for the same reason it doesn't know that it is a body. Bodies don't know anything.
Sure. That still won't be useful for astrology.
nod "similarly to you but not exactly."
For me, people with special virtues age in a different manner. The nature of their aging is different. Also, time is harsher on some people than on others. If a spell is purely about the body, it can detect Decrepitude, it can detect the health of the body, the state it is in, its "weathering," the actual effects of time. But if a spell cannot detect where it is, why should it objectively detect when? And the likely effects of future aging rolls is IntellegoGameMechanics.
Anyway,
Ken
BTW, the mechanical effects of aging are not completely about the body; the mind also affected.
The form for Astrology is Vim, not Corpus, though.
Age is different than Aging than is different from Apparent Aging.
Hmm. So the spell to determine a person's time of birth is published as InVi?
Agreed about Age. Since Age is purely about time, whereas the other 2 are about the body, maybe InCo only detects those 2.