No, don’t rule yourself out because of age. There are no age limits to register. There have been many successful transplants from donors over the age of 50. According to organdonor.gov, one of the oldest organ donors in the U.S. was 92, and his donated liver saved the life of a 69-year-old woman!
Likewise, people under age 18 can also register to be donors. Parents may legally revoke the registered decision of a minor to be a donor until that individual turns 18. It is especially important for minors who wish to donate to discuss that decision with their families.