kaji's age

Shaun was telling Kaji that he's old and then he starts making fun of him because of it.

Shaun: (To Kaji) Ha ha you're old.  (To me) How old is he again?
Me: '04.
Shaun: So 8.
Me: No 7
Shaun: Yeah 8.
Me: No because his birthday is in December.
Shaun: (To Kaji) You're old. You're 35.
(I give him a weird look.)
Shaun: Is he? No he's 49.
I'm still looking at him weird to see if he'll second guess himself.
Shaun: 49.... right? Do you know?
Me: Yes.
Shaun: Is it 49?
FINALLY he does the calculations himself to find out that he was right awhile ago.