As a Best Man Speech Writer I have a gifted insight in to how grooms operate the world over. I know that the Empire State building is pretty much de rigeur when it comes to proposals, I know that well over 85% of my clients still ask for permission to marry from the father and I know that from the minute the button is pressed the girls take over and you become a passenger on a rather fast, furious and pricey roller coaster ride.
So, pretty much all the groom has to do is choose a best man and organise the cars, except when I say choose...it's very much one of those situations where there IS a loaded revolver to your head and it WILL go off should you make the wrong decision. There are expectations from your wife to be and your family. One doesn't want you to ruin everything by choosing the close friend she's never liked with the potty mouth and drink issues, and the other wants you to choose your brother. So you choose your brother.
This of course keeps both parties happy but doesn't necessarily make anything easier for you, as most brothers won't have lived or indeed socialised together for many years by the time the wedding comes around. In fact the only really good stories he has about you are over 25 years old and he really hasn't got know your girlfriend yet as he lives in Australia. This is a very familiar scenario for me when I'm writing best man speeches. Over 70% of the best man speeches I write are for brothers and they do bring about their unique issues - mainly that they know very little about the groom's real life after the age of 18.
This is not as worrying as it might first seem because I never really use anecdotes anyway as they're boring, exclusive and not usually that funny, so you're forced to think of things in a different, more inclusive and hopefully funnier way. Actually this is how every best man speech should be written - forget the anecdotes and tell a story instead. We don't care about EXACTLY what happened in his life to date, I want daftness, I want fun and I really don't care about detail. So don't worry about not having any information on your brother past the point of puberty - it doesn't matter.
Instead think about what his dreams were, think about what kind of character he used to be growing up and think how you can use that in a funny way. What were his hobbies, passions and disasters? Put your thinking cap on and make that funny. A good best man speech for a brother should be written in exactly the same way as that for any other best man - with warmth, intelligence and a great dollop of imagination.