According to the U.S. Department of Health & Human Services' organdonor.gov, whether or not your organs can be donated is determined at the time of your death. While there are a few absolute restrictions (such as HIV infection, active cancer or systematic infection), generally your medical history doesn't matter. With my cystic fibrosis, there's no way my lungs, liver or pancreas could ever be used because of systematic infection, but, it doesn't affect my heart or corneas, which are in fine condition to be donated.
As for the age of a donor? According to both CORE and organdonor.gov, you can never be too young or too old. Newborns can be registered organ donors, as can senior citizens.
If you're of age to have a driver's license or ID, a quick trip to the DMV can make you a registered organ donor. If you are younger than that, let your family know your wishes so they can give consent if anything were to happen to you.
Finally, there's one other pesky thing that can stop people from wanting to donate their organs: religion. Again though, both CORE and organdonor.gov report that most major religions view organ donation as either a wonderful and charitable thing or leave it up to the individual.
On organdonor.gov, there is an extensive list of religions and their views on organ donation. I am only going to use a few examples from that list. If you're of a faith not addressed below, simply visit the website or talk with the religious leader at your place of worship to clear up any questions you have about your faith and organ donation.
Catholicism and Christianity both view organ donation as an act of charity and love. The Vatican considers transplants to be ethically acceptable, while the General Assembly of the Christian Church adopted a resolution in 1985 that encourages "members of the Christian Church (Disciples of Christ) to enroll as organ donors and prayerfully support those who have received an organ transplant."
Judaism echoes this, as it sanctions and encourages organ donations to save lives. The Conservative Movement's Committee of Jewish Laws and Standards states that not only is organ donation after death an act of kindness, but it is also a "commanded obligation" to save lives.
According to organdonor.gov, as of this writing, 117,110 people are awaiting an organ transplant. Eighteen people die each day waiting for one.
But you can help. A single organ donor can save up to eight lives.For more information, visit core.org or organdonor.gov. To register to become an organ donor, visit donatelife.net.