The book and movie, My Sister's Keeper introduced many people to the concept of organ and tissue donation and transplantation, which is a complex process that most of us know very little about. There is an Organ Donor Web site that answers many questions and encourages people to sign up to be a live donor, or a donor after an accident.
There are about 103 thousand people waiting for an organ donation in the United States right now, and there have only been nine thousand transplants completed this year (through April). Most people can be a donor of blood, stem cells, tissue, and blood for people who they "match."
You are never too old to be a donor and if teens want to register as a donor, they will need parent permission, but can sign up at their state registry. There is always a need for minority donors, so, please check out the Organ Donor site and think about saving someones life.