Look at the example magi on ArM5, pg24-28, they certainly don't have an additional 225xp for abilities in addition to their 240xp for apprenticeship.
Reading the Example, Darius of Flambeau on page 31-32 shows that Darius only gets the 15pts of xp per year of later life for each year before apprenticeship. Once he begins apprenticeship, he only gets the 240 xp for that 15 year block.
So, for a 23 year-old magus with the Skilled Parens virtue that completed his apprenticeship at age 23, you would have:
native language 5
childhood xp: 45
later life xp: 45
Apprenticeship: 240+60 (skilled parens)
Childhood and later life xp could be spent on General abilities unless you had virtues or flaws that permitted other academic, arcane, or supernatural abilities. (I guess you could have a child warrior or branded criminal, and take martial skills, as well.)
You do not get the later life xp for the time spent in apprenticeship. You have to divide that apprenticeship xp between the Arts and the (Arcane) abilities needed to be a magus-- Latin, Magic Theory, Artes Liberales, Parma, Concentration, Finesse, Penetration, Code of Hermes, Order of Hermes Lore, Profession Scribe, any other appropriate lores, like Fae, Magic, Infernal, or Divine. Remember, you need a score of 5 in a language to write a book in that language.
A possible breakdown might be: Latin 4 (50), Magic Theory 3 (30), Artes Liberales 2 (15), Parma Magica 1 (5), Concentration 1 (5), Finesse 1 (5), Code of Hermes 1 (5), Order of Hermes Lore 1 (5), Profession [Scribe] 1 (5), Magic Lore 1 (5) for a total cost of 125 points.
With Skilled Parens, that leaves you 175 points to put into Arts, perhaps giving you 5 arts at 6, 4 at 5, and one at 4. Standard apprentices would only have 115 points for Arts.
This does tend to make apprentices created in-saga more powerful than initial characters-- teaching qualities, access to books, adventure experience, etc. All of it can result in a feasibly more potent finally gauntleted magus than the stock creation process.
Take a look at Koresh of Flambeau on the sanctum hermeticum site:
geocities.com/sanctumhr/Spec ... oresh.html
(although it does have one minor mistake-- Koresh's pater's teaching quality goes up by one after his Age 10, Spring. [Possibly by 2, as Darius could specialize in one-on-one teaching to give himself an effective teaching quality of 10 {-1Com+2teaching+3+6singleStudent}ArM5 pg164] and then again by 1 at Age 15. Finally by 1 more after his final season at Age 22. This changes his scores slightly over time.)
Hopefully this helps.
-Ben.
nonono, I want that apprentice in the lab, earning his keep and increasing my lab total as much as feasible. This is no laxadasical vacation through community classroom, we're working magic! 
He'll be getting as much pertinent education as quick as we can, and then he's measuring components, scribing notes, assisting in experiments and enchantments. He might be a magus' legacy, but no one wants the reputation of being a cupcake. If that apprentice has time for training with the turb then the magus had better be some kind of very martial oriented wizard or incapacitated for some reason. Martial skills are what the grogs are for. Well, grogs and hoplites.