Yuvraj is the son of Yograj. I'm sure the year he was born was maintained in some record. Wouldn't have been able to fudge it.
Yes, but back in those days especially north India where ambitious parents want their kids qualifying for age group tournaments, the fudging is rampant. In that time, the background check wasn't AT ALL enforced.
In bihar and UP and some other places, age is understated for government jobs etc purposes. It's all pervasive.