Commentary:
That's not a slip of the pen: Dalris is a bard, the AD&D character class. Strap in while I drop some four-decades-old knowledge.
Hush, don't say that word, it might attract a Snarf!
After a few days away, it's time for me to resume my favourite activity: nitpicking.
To even qualify for the bard class you needed MINIMUMS of Strength 15, Dexterity 15, Constitution 10, Intelligence 12, Wisdom 15, and Charisma 15.
There is no way you rolled those ability scores on 3d6 in order unless you cheated like a madman.
It was like Paladin, the character class no one had every played where someone was witness to the character creation?
The odds are 0.00001723277% That's a character in 100,000. There are, according to probably unfouded rumours, 50 millions persons who have played D&D ever. Even if they somehow all played D&D 1e and stopped there, that would be 500 bards ever. Well worth the price of the paper to print the class.
And let's ask again: how old is Dalris?
Suppose she began her fighter-ing at age 16, the absolute youngest age a 1st level human fighter could be according to the AD&D Dungeon Master's Guide (page 12). She's a prodigy when it comes to fighter-ing and reaches level 5 in just 1 year.
She goes off to be a thief. She's also a prodigy at thief-ing and reaches level 5 in that class in just 1 more year. She's now 18, one year YOUNGER than the minimum 1st level human thief age according to the DMG, but we’ll allow it.
Dalris then studies druid magic with her dad and due to nepotism and favoritism, passes her bard classes in a week (hey, it worked for Carr with magic-user classes!), so she's still only 18.
Then for some reason Dalris studies magic-user magic with Landor. Maybe she doesn't get very far or maybe Landor dies soon after she starts, so maybe only another week has passed. Dalris is still just over 18 years old.
But that was FIFTEEN YEARS AGO. So she's 33 years old now. And this is assuming the most favorable possible advancement rates imaginable.
Although I will note that per the AD&D DMG, the minimum age of a 1st-level human magic-user is 26, and Carr is only 15, so we're not playing by the rulebook when it comes to character ages in this series.
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An addition with the benefit of hindsight that will be seamless to readers, but was actually written several days after the above.
One of my old-timer friends pointed out that it didn't take anywhere near two years to reach level 10 or 11 in an AD&D character class. With regular play, assuming your character didn't die, and pretty much all you did was enter the dungeon, kill monsters, grab loot, rest in town, repeat -- you could easily reach level 5 in a couple of weeks of game time and level 10 within several months.
While I agree that she could conceivably level up quicker than a year for 5 levels, which is totally possible -- even with 5e's rate, an adventuring day is a day, so one could reach level 5 in a month. On the other hand, wasn't there a rule that you needed to get money to get xp? Is she sitting on top of untold riches or couldn't she just get a gift from her wealthy father to jump up 5 levels? "Daddy, I wanna be a level 5 fighter" "Here is a cheque honey". Or he could gift a random rat a few tens of thousands of gp if they needed to be looted from the dead body of your enemies (I know for sure 1e had some strange loot so a rat owning money wouldn't be out of place).
Put there is no way she could be a bard so young: she'd have to wait to get the thief minimum age of 19 to reach level 1 and get her other level-boosting cheque. Maybe there is a requirement of legally buying a glass of liquor from a store to get that first level? I think the minimum age rule should apply. Sure, she isn't 26 and neither OUR Carr when we start school, but the minimum age for a character is to be a 1st-level magic user. She didn't mention that she graduated magic with Landor, only that she started training, which she could have from a tender age -- maybe even before starting fightering and thief-ing. Along the same line, (1) we can't discount that Carr is 26, and suffers from amnesia about his youth (2) he isn't yet a 1st level magic-user. As far as we know, he didn't gain any xp yet.
She's a minimum of 34 years-old. A grandmother in the Middle Ages.
That just leaves her claim to have studied magic with Landor. As my friend pointed out, maybe Dalris exaggerates this claim the same way she exaggerates her claim to be a direct descendant of Bhukodian / Kandian royalty. "Studied magic with Landor" might mean that baby Dalris drooled on the pages of Landor's spellbook while she cooed on his lap, or maybe toddler Dalris looked at pictures while Landor was preparing his spells for the day.
That's my head canon.
Dalris, age 3: looks at picture in Landor's spellbook and resolve to be a spellcasting princess when she's all grown up.
Dalris, age 4: learns that Landor passed away. She doesn't care anymore.
Dalris, age 6: starts thief training after seeing an episode of Robin Hood.
Dalris, age 9: starts fighter training after seeing an american football match.
Dalris, age 19: speaks with her father about her career, cashes a cheque to reach the required level overnight and conclude she's heard enough of her dad's rambling to validate bard level1.
19 is a reasonable age for OUR Carr to be, unless I am mistaken, so they are a perfect match.
Or, heck, maybe Dalris was an incredible prodigy like
John Stuart Mill, who was taught Greek at age 3!
Plato started earlier!
As for the tower climb: the specifically described window means that anyone could use that window of Landor's room to bypass the murder door to gain access to the ultimate magical power stored within.
Bonus point for that door being visible from the court yard. I am not sure about druid in 1e to be honest, but couldn't her father just turn into a bird? Didn't they have animal forms? Or couldn't he cast Shapechange?
In a gamebook path we didn't take, Beldon uses the Fly spell. Beldon didn't need to wait fifteen years after Landon’s death for Carr to show up to get into Landor's quarters. Beldon could've entered Landor's quarters fifteen MINUTES after Landor’s death.
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We'd better stop asking questions before we fail a bunch of Sanity checks and have our Wisdoms reduced to 3 like Carr.
WIS 3 is the reason why Beldon failed. But it's established that Dalris is WIS 15.