NOTATION
ON AGES:
Charmed Life:
"Cat admired his elder sister Gwendolen. She was a witch. He admired her and he clung to her. Great changes came about in their lives and left him no one else to cling to." PG 3
Cat and Gwendolen are orphaned during a paddle steamer accident. When going through their parents' belongings with Mrs. Sharp, they discover letters from a man called Chrestomanci:
"The first was dated twelve years ago, soon after his parents had been married." PG 9
"The third letter was dated six years ago". PG 10
These letters are explained in the ending scene by Chrestomanci himself:
"I'd no idea he was Eric Chant, or any relation of mine at all--though I suppose I might have remembered that his parents were cousins, which doubles the chances of their children being witches. And I must confess that Frank Chant wrote to me to say his daughter was a witch and seemed to be using her younger brother in some way. Forgive me, Cat. I ignored that letter because your father had been so very rude when I offered to make sure his children would be born without witchcraft." PG 258
As such, we understand that twelve years ago (from the time period of the first chapter) Frank and Caroline Chant had not yet had children. Obviously, of course, as they were just married. Even if they immediately set out to reproduce (which is probable, given the time) Gwendolen cannot be more than eleven at the start of the book. Cat, who must be at least one year younger but probably more, given their dynamic, is nine or ten.
Of course, at least half a year passes during the first chapter.
"Gwendolen made excellent progress. Such a promising witch was she, indeed, that she skipped the First Grade Magic exam and went straight on to the Second. She took the Third and Fourth grades together just after Christmas and, by the following summer, she was starting on Advanced Magic." PGS 12-13
And, given that the steamship accident happens on "a hot day" with the steamer "crammed with other people in holiday clothes" for the "day trip down the river" PG 3, one might assume that it went down in late Spring, Summer.
By this sloppy math, we can judge that exactly a year passes from the accident to when the story really gets going. Gwendolen is still just beginning Advanced Magic when she arrives at the castle and is told she cannot go on learning. As everything within the book happens within a few weeks, as Summer is becoming Fall (given Cat's wishes for the chestnuts, and the apples being in abundance), Gwendolen and Cat are really only a year older--
So at most, Gwendolen is twelve, and Cat is ten or eleven. Or younger. He could quite easily be younger, given that another half year passes before he meets Tonino and is offended by his comparative youth. See below!
Wherein it is assumed that the Fall-Winter-Spring events follow immediately after the events in Charmed Life.
The Magicians of Caprona:
"Rosa, who was eight years older than Paolo and quite grown up even then," PG 8
"Tonino agreed, because he was more than a year younger than Paolo and valued Paolo's opinion, but it always seemed to him that it was Paolo who was the true Montana." PGs 11-12
And finally, chapter two leads into chapter three with noting how things are wrong in Caprona, therefore it's recent time, with everyone extremely worried.
"Rosa was now eighteen. The entire Casa was busy discussing a husband for her, and there did, now even Paolo noticed, seem to be more fuss and anxiety over the matter than there had been over Cousin Claudia, three years before." PG 33
Rosa 18 - 8 = Paolo 10 - 1.??? = Tonino 8-9
Most of the action goes on during that time period, with some time passing as it notes that "all that autumn worry grew" or some such phrase (34?), and then the bridge breaks, and three weeks of fixing, and I believe Rosa marries Marco just after Christmas. After New Years Marco is introduced in the Montana house. ANYWAY more than a year doesn't really pass, so Tonino really can't be more than 8-9 when he goes to Chrestomanci castle.
Cue Stealer of Souls:
"Cat looked at the Italian boy, and the Italian boy held out his hand and said, "How do you do" in excellent English, but with a slight halt at the end of each word, as if he was used to words that mostly ended in o. Cat knew at that instant that he was going to count the days until someone took Tonino back to Italy again. And he hoped someone would do it soon.
It was not just the beautiful English and good manners. Tonino had fair hair-that almost grayish fair hair people usually called ash blond-which Cat had never imagined an Italian could have. It looked very sophisticated, and it made Cat's hair look a crude straw color by comparison. As if this was not enough, Tonino had trusting brown eyes and a nervous expression, and he was evidently younger than Cat. He looked so sweet that Cat shook hands as quickly as he could without being rude, knowing at once that everyone would expect him to look after Tonino." PGs 28-29
TO BE BEEFED UP WITH EVEN MORE QUOTING OF QUOTATIONS.