This does not pretend to be a historical essay by any means, but more like how I see the 'career' of a knight going in different parts of his life, and pretty much how we do it in our Campaign. Feel free to comment and expand how you do it. :)

The starting point:
This focuses on the sons of a vassal knight, as the household knights and knight errants generally do not marry (holding out for an heiress, Lord unwilling to pay for the upkeep of a wife or simply because they can't afford to have a family and still feed their horse), and esquires' eldest sons, while possibly making to the squire level for household knights, would be unlikely to ever be knighted and probably become esquires themselves. The sons of Lords would naturally warrant a space higher up in the chain, in the court of the king for example.

The sons of a vassal knight generally follow the old adage of The Heir, The Spare and the Prayer. That is to say, the first-born is trained as the next vassal knight, the second-born is trained as a knight in case the eldest dies, and the third goes to the Church. Fourth and subsequent sons would be more akin to esquire's eldest son, and more likely to become an esquire rather than a knight. Depends on the wealth of the father, of course, how many sons he can afford to outfit as knights.

1. Page, 9 - 15 years old
(historically, I think 7 - 14 was more usual, but these are only generalizations)
The young sons of noblemen are usually fostered out to family friends (spares, more likely) and liege lords (heirs, more likely). Needless to say, this depends a lot on the fraction of vassal knights to household knights, i.e. how many vassal knights' sons are looking for a position. If vassal knights are 'rare', like 1/6 like Greg was proposing in another thread (which tallies at least as a ballpark number from what I seem to gather from the fact that having lands was a big deal), then there are fewer sons and likely all might be accommodated by the liege lord. If there are more, then the liege lord would be more inclined to look after only his most significant vassals' heirs, and the rest would go to other vassal knights (friends, allies, famous/important men). The boys would act as pages, serving the fostering host and hostess, learning the courtly etiquette and making connections with other young boys (friends/enemies) and older ones (potential mentors, patrons).

2. Squire, 15 - 21 years old
(historically, I think 14 - 21 was closer to the 'usual')
See the caveat in page re: the fraction of vassal knights. The heirs might be placed with the Lord and the most famous of his household knights, and then to the most important other vassal knights. The knight-squire bond is very important and might lead to a life-long mentorship/patronage, so it behooves the parent to try and find a good knight to pair especially his heir with. Even with the spare, it might be time to try to play politics, although of course family friends are always an option, too.

3. Knighting? Not so fast...
Heirs: The knighting of the first-born is one of the Four Universal Aids, so the peasants of the vassal knight daddy should be paying for this. But what then? Daddy is still alive, but the manor cannot support two knights. This is where having so few vassal knights compared to the household knights comes real handy, as it is much more likely that the Lord can find household knight slots for all the heirs. After all, it allows him to make sure that they have no conflicting loyalties later down the line, foster loyalty towards him through patronage, and gives him a good chance to see the character of the future vassal knights first hand. If there are simply not enough slots, the Lord would likely save them for the significant heirs (multiple manors) and other such, while the knighting of the rest might be deferred until the inheritance is more imminent. The Lord might also try to arrange household knight positions for some of the knighted heirs that he can't support himself, preferrably in a friendly court (so that he can ask a favor and there is likely no hard feelings when the heir is recalled to his inheritance) far away (so that any later loyalty conflict is rarer). In Pendragon, I see heirs getting knighted almost always, and sent off to become knight errants, to get some reputation and experience.
Spares: Likely not knighted instantly, if only because the father cannot afford the cost of an extra set of equipment. They might be sponsored by their knight, or even the Lord (especially likely if the Lord has need for household knights, which might indeed be the case with a 20/100 split) if they are worthy of it. In our campaign, the spares usually are knighted as the father dies and gives his old equipment as inheritance to the second son to make their way in the world. After being knighted, these men are likely looking at a life-long career as a household knights, although they might have to work to get the position in the first place.

So where do household knights come from?
- extra sons of rich vassal knights
- heirs of the vassal knights
- spares of the vassal knights
- fourth sons and particularly promising sons of esquires
- very rare gifted commoners who might get squired and then knighted by a patron

The exact mix depends a lot on the economics, as pointed out earlier. If vassal knights are the norm, then each Lord has fewer household knight slots available and there are more heirs running around, which makes things tough for the spares. If the split of vassal/household knights is more even, then that is good for spares. If the household knights overwhelmingly dominate, that is very good for the younger sons, who now have a chance for knighthood, too.

I think it is a good assessement.

In my campaign knighting is a serious business, so knighting of younger brothers or sons requires some politicking to achieve. This is usually done through gameplay.

My research has also suggested 7 and 14 as the starting ages for pages and squires, respectively. Ian Mortimer supports this idea in the his excellent "Time Traveler Guide the Medieval England" (mentioned recently in another thread), where we specifically says boys were taught to fight from age seven. Another author I read talked about the symmetry of 7, 14, and 21 as the major milestones in a knight's career. And of course, there's the mystical and poetic aspects of the number 7, which appeals to me. Anyhoo, I was able to sell Greg on the idea and that's what you'll see in Book of the Entourage.

I also read that pages usually went to the court of their father's liege lord, or to an uncle. From Knights in History and Legend: "Maternal uncles were preferred to paternal ones. Because inheritance went preferentially to men, a father's brother could well consider that his nephews were his rivals. But a mothers brother was happy to establish a close relationship with young relatives without entertaining any thoughts that their inheritance ought to be his."

I highly recommend this book:

http://www.amazon.com/Knights-History-Constance-Brittain-Bouchard/dp/1554077559

It is lavishly illustrated and has about 25 scholarly essays from various PhDs in England and the States. Usually I don't expect much from these kinds of mass-market books, but this one is quite good.

FWIW.

Evening folks,
<Makes folklore roll - standard success>
My Dad left school at 14 [the traditional age] in England in the early/mid 1950's. Whereupon he went to work as an apprentice Joiner, for the standard seven year apprenticeship. He ceased being an apprentice at the age of 21, the traditional age of adulthood. It is my impression that most traditional occupations/crafts still followed this structure at that time.
This was in an era when crafts were giving way to/becoming/already become industries but the traditional structure always seemed to me to be a continuation of the craft guild structure of the late medieval period. It would not surprise me if this same structure applied to all boys equally across social classes and we could therefore accept 14/21 as standard.

I don't know how valid the comparison is timewise, applying pre-industrial to medieval. Or how valid it is demographically to stretch from buroughs to castles; but it feels like it fits to me.

GR