if you think that's a little odd, read the accompanying course notes! ;)
This sentence is confusing, feels like it's missing something.
A 的 phrase can stand in for a noun in Chinese. Or rather, the noun for said phrase can be omitted (in this case: 人/老师), especially if it appears twice in the sentence, similar to how we use "the one(s)" in English.
A rather strange way of saying relatively anything
In English "one" is optional in comparative sentences like this. But if it's included it can never be written as the numeral "1" as Duolingo suggested to me.
Sounds like yoda
'The younger one' = 'is younger than the others'
this sentence is so confusing to translate bc the english comes out as a fragment oof
Younger = younger than [unnamed others]
的(de) sounded like 个(ge) to me on this sentence.