An attempt at a timeline.
- a long time ago: the Kingdom of Bhukod flourishes throughout Tikandia
- ~500 years ago: Bhukod falls, for unknown reasons
- ~200 years ago: Tikandian rulers begin searching for the Sceptre of Bhukod
- "more than" 40 years ago: Landor founds the "College of Arcane Sciences", also known as "the academy"
- ??? years ago: Landor meets Thayne and takes him on as a student
- ??? years ago: Landor meets and marries Marla; takes Beldon on as a student
- ??? years ago: Landor finds the Sceptre of Bhukod
- ??? years ago: Thayne departs the academy
- ~15 years ago: Carr is born to Landor and Marla
- ~15 years ago: Landor is pursued by Archcleric Oram's goons
- ~15 years ago: Landor dies, "shortly after" Carr is born
- 2 years ago: Carr and Marla escape from Saven (on the mainland) to Seagate Island
- one week plus 5 days ago: Marla gets sick
- one week ago: the gamebook begins
- today: Carr reaches "the academy" gate
Let's focus on the items including and between ~40 years ago and ~15 year ago parts. (Or however old you think Carr should be: he could be 12, or 15, or 17, and it doesn't fundamentally change anything.)
How old was Landor when he founded the academy? Let's say at the youngest he could've been about 20 -- clearly he was a prodigy, but even prodigies need time to amass funding (from where?) and so forth.
For about 25 years, up until Carr's birth, Landor was doing his thing at the academy. Teaching students. Paying taxes. Avoiding press gangs. Debating policy with other faculty members.
This means Landor was about 45 years old when Carr was born! Thus Marla was probably considerably younger given that D&D-land didn't have advanced medicine to allow 45-year-old women to have babies safely. This lends credence to the May-December romance we postulated earlier.
We could say for sake of argument that Marla was 18 when she and Landor got together (to keep their relationship legal in most states) and close to 19 when Carr was born. That means that if we stick to Carr as 15 years old, Marla was about 34 when the book started.
Or, who knows? She could've been 44 when she married Landor and 45 when Carr was born -- the same age as Landor. (Maybe clerical magic allows older women to give birth safely?) And then Marla would've been 60 when the book started. Which might explain why her illness finished her off. Although a severe illness to someone malnourished and living in a cold shack for the last two years could kill anyone.
Back to the timeline.
Prior to Carr's birth (else Thayne would have known for sure that Carr existed rather than needed to peer at Carr's facial features), Landor also discovered the Sceptre of Bhukod, showed it to Thayne, which triggered Beldon's jealousy, which caused the falling out between Thayne and Beldon, which caused Thayne to depart the academy. All of that happened before Carr was born, roughly in the order listed above, so that cause-and-effect makes sense.
That is A LOT of backstory!
Note also the gap between Carr's birth / Landor's death roughly 15 years ago and Marla's / Carr's flight from the mainland to Seagate Island roughly 2 years ago. What was Archcleric Oram doing in the intervening years? Oram gave up on the Sceptre of Bhukod even though Landor's widow was still in Saven where Oram also resides?
What was Beldon doing all this time?
What does Carr remember from his childhood?
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One final question: why did Landor, "Archmagus of Saven", found his academy not in Saven, but in the pirate-infested Freeton across the water?