My brother's 11 and I'm telling him that I always wore briefs at his age but when I came home with a packet of 5 briefs for him he said he wouldn't wear them. Apart from the obvious look, what is the difference for all age groups between briefs and boxers?

The difference is personal preference, does one prefer tight fitting or loose fit around the genitals.

Briefs have a leg band (sometimes with elasticity) that angles from the hip into the crotch. Boxers have a leg that goes down the thigh and hangs loosely. There is a hybrid, boxer-briefs, that are a snug fitting knit but with legs down the thigh.

The differences other than appearance is personal preference. Briefs may be more prone to chafing and rashes, especially when there is a weight issue.

How old are you, and why are you buying your brother briefs ?

To be honest, at least in the US, boxers are considered more stylish than boxers.

Chuck, fix your redundant answer.