[Jack's not really bothered by age differences himself - it's more about the other person's perception of them and he's pleasantly surprised by Euphemia's apparent confidence here. He'd expected her to be flustered and blushing, but this is much more enjoyable. He doesn't prolong the kiss any longer than necessary, but he doesn't give any half-measures either.
By the time the water gushes away from them as the bubble disappears and confetti starts to drift down into the water, there are things happening in his Speedos again that mean he's not going to be getting out of the water again any time soon!]