There’ a website called The Real Me. It’s got a free test to see what your ‘metnal age’ is vs your actual age. The test defines “mental age” as your psychological abilities compared to the, quote, “number of years it takes for an average [person] to reach the same level.” It’s 30 questions, mostly true or false. Things like, “Could you kill a cockroach with a book?” and “I like to be friends with [people] older than me,” true or false? At the end, it tells you your mental age. Like, you might be 42, but your mental age is 26.
Try it out!
https://www.arealme.com/mental/en/
