I'm 27 and started four or five years ago. Not the age group you're shooting for, but hopefully my input is well received. It seems that regardless of age, some people are motorcyclists and some aren't. You never know until you try.
The older I get, the more I try to get lost on back country roads and then navigate my way back to a familiar area. It is very nice to leave everything (work/family/life) behind and escape. It has become a form of therapy for me.
A lot of the time newer riders sell their motorcycle due to financial responsibilities and then never get back in the saddle for one reason or another. Those are the types (possibly like your brother) that simply lose interest and find another hobby. Others have a fall and are too timid to jump right back on. There are also those who have a scare and pack the bike away because their health is too much to risk.
If life provides you the opportunity to see the world through a visor, I strongly suggest you take it. Everything looks different when you're on two wheels. You smell the air. You feel the temperature change. You watch the clouds. You become a part of your surroundings. This is especially true if you do any type of 'touring.'
I primarily ride sport bikes. I do 50 to 100 miles most days taking the long way home from work. My free time on the weekends has a 400 mile minimum each day. I commute on my motorcycle, grocery shop to a certain extent, run errands, and use it for anything that I safely can rain or shine. I consider myself a motorcyclist, not a fair weather hobbyist. I've crashed, I've had scares, and I've had financial troubles. But nothing will take my motorcycle away, it is far too dear to me.