I have heard kids from 6 to 80 years of age say this.
I find it sort of embarrassing for him. It'd be like if my Dad said, 'Dude - that's fuckin' huge...' and my mom answered, 'totally'.
I'd look at them and think - 'why're you trying to act like you're twenty - or thirty - or even forty...wait - how old are you again?'
Are we supposed to take these people seriously or not? Do they want anyone else to?
(And I'm totally non or bipartisan in my embarrassement for people who seem determined to act younger and cooler than they are).