Obviously I'm not suggesting all mature students are hyper-intelligent, but I do think it's not as easy to tell as it might seem to be.
Old people have been bitten by the “A 95% inference will be wrong 1 in 20 times” thing a lot more, and also have been exposed to a wider array of experience where they might often judge an inference as being less certain than someone with a narrower range of experience would.
I don't have a specific reference but if you google it, you should find what I mean.
different abilities at different ages, on average, but IIRC, some as early as late teens, some as late as the 40s.
EDIT:
Actually, some as late as 50+. https://blogs.scientificamerican.com/beautiful-minds/when-do...
A 40 year old mature student was last in school more than 20 years ago. Younger students were last in school as recently as 1 year ago. Learning is a skill and it's perfectly possible to be out of practice. There may also be some knowledge gaps because recent practices and knowledge are different to common knowledge 20 years ago.
It's also possible that mature students are more assertive about asking questions.
And also - what some of the students in a class consider "obvious" is not at all obvious to all of the class.
Of course if someone is showing clear evidence of dementia, that's a different issue.