The narrator explains his way of talking to adults, and then:
And that adult feels that he has been able to get to know a person with good hobbies like his own, and ????
I can't understand the last part (ごきけんになるわけだ).
Firstly, I assume the adult wouldn't put ご on a word referring to himself so I guess ごきけん is the narrator. So maybe I can translate it as:
surely he (the narrator) will become a distinguished person.
But I'm doubtful. Isn't it a bit self-serving for the narrator to assume that adult would add the honorific ご? These things confuse me a lot. Maybe my translation isn't even close. I have no confidence about this.