Just listen to that cry of pleasure. He doesnt cry out like that during his third climax. The third will still have been very plesurable for him ... but less intense than the first and second. He would have to wait until tomorrow for the next VERY very intense orgasm.
Most people older than their twenties either don't have the need for so many ... or they can't do it. When we discover orgasm for the first time the feeling is so mind numbingly incredible (it still is when we're much much older!) that we want an orgasm several times a day. His young cock makes up for its small size by 'rewarding' him with pleasure and multiple orgasms in a short period of time.