What could be said of a person who judges people on basis of whether their interests are kiddish or mature. For example, someone at age 30 likes playing video games and he is ridiculed saying "Wow, you play video games at 30, are u a kid". What would you call this person or this judging.
A one-sided judgement?
Not a teacher.
ageist (or agist).
Pope of the Dictionary.com Forum
They should, of course, say "Wow, you play video games at 30, are you a kid?"
I would say they were being judgmental.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.
"What would you call this person or this judging."
I understood that the OP already knows that this is judgemental.
How about supercilious?