You're heavily speculating about a person, just to write - essentially - a fictional story you happen to like. Your comment is ageist, nothing else.
False, this is your opinion, they were careful not to state what is, but what might be the case.
PS: As an aside, to be very pedantic, the word ageist is a subjective term, not objective. You can say that 2+2=4 is literally true, but can you fairly say that anything is literally ageist when that's subjective? Just something to noodle over about what that word even means.
Your respectfulness or lack thereof is almost totally irrelevant to if your post is ageist. I don’t see “ageism” as a very useful word anyways since my attempt to narrow the definition makes it painfully subjective.
It seems like most people would agree with your examples.
Do you view this sort of ageism filter as a useful tool for understanding the world? Does the word ageism automatically imply a negative connotation then?
Would you turn down getting lectures from Donald Knuth even if he's older than dirt?
Using age as one tool to understand a complicated world with incomplete information seems fair, but I think you have to judge the individual on their own merits and abilities or you can miss out.
There's a difference between giving lunchtime lectures and teaching an entire course while assigning grades that affect the careers of young people.
You managed to contradict yourself within the same sentence.