An organ donation directive records your decision about donating organs and tissue, and whether you want to place limits on it — donating some organs but not others, permitting research or education use, or declining entirely. It can be registered with a state donor registry, indicated on a driver's license, and stated in an advance directive. Most people who intend to donate use more than one of these.
Timing is what separates this from every other estate document. Organ recovery is viable only within a narrow window after death, and usually only when death occurs under particular clinical circumstances. A will read days later has no bearing on it. The decision has to be discoverable by hospital staff immediately, which is why registries and license designations exist.
Your family's role varies with where you are and how clearly you recorded the decision. Many states treat a properly documented registration as legally binding, so it should not need family consent. In practice, hospitals often still consult next of kin, and relatives who were never told sometimes object. Telling the people close to you what you decided prevents your recorded wish becoming a bedside argument.
Common reasons people rule themselves out mostly do not hold. Age is not an automatic barrier and many conditions do not disqualify donation — suitability is assessed clinically at the time. If your view has changed since you last recorded it, update the registry and your directive rather than assuming an old designation lapsed.