Ha ha this is cute. It has been a while since I put my Japanese into use but here is a translation. I hope it helps^^

Jaejoong:One song?
~~sings~~
Jaejoong: Do you know this song?
Crowd: Yes!
Aitakute aitakute…
(Yoochun doesn’t sing )
Jaejoong. You’re bad/cruel Yoochun.
Youchun: W?
Junsu:W.
Yoochun: Rather than that song I like Itsudatte Kimi Ni better
Jaejoong: Ah that..
Yoochun:?? (I can’t hear Yoochun clearly)
Jaejoong: Then…
~~Sings~~~~
Jaejoong: Yes. I still remember it.
Crowd: Thank you!
Jaejoong: Compared to the newcomers who debut in Japan now, we are probably a bit older. Well they are 22, 23 years old, right. But well, we’re still alive (can go on) We are still healthy, we can still be of use.
Fans laugh
Jaejoong: No no, not like that.
Yoochun: Is that the problem?
Jaejoong: No not that. Well, we have the confidence to make you laugh, to move your heart. We can still dance and run. We have to confidence to keep going on steadily. (Laughs)
Really that “being of use” doesn’t mean that.
Yoochun: If it doesn’t mean that, what does it mean?
Jaejoong: Laughs
Yoochun: What in the word does it mean?
Fans: Dou iu koto?
Jaejoong: “Being of use” you know, we don’t have time, well…
Yoochun: You got stuck, didn’t you?
Jaejoong: it has various meanings. Sorry. (Laughs) Don’t laugh please.
Fans: Dou iu koto?
Jaejoong: Shouyuu koto

credit:shiroi @JYJ3