You are only young once, but you can be immature for a lifetime.

You're only young once, but you can be immature forever.

Life is so unfair that one is more likely to get into some sort of trouble than be rewarded if one attempts to do a good deed; many times one spends time and resources to help someone only to be totally ignored with not so much as a thank you.

You can celebrate birthday every year and fights like this (with Morales) comes once in a lifetime,

They were preparing a nice meal for Dayna Curry, whose birthday was on the 4th (of November), ... Over the past few days it had been relatively quiet in Kabul proper and I think emotionally they had all come to develop a sense of resignation that they were in for the long haul, that they were doing OK emotionally but they certainly did want to get out of there as soon as they could.

He's a young, immature boy used by older and cynical criminals.