Let explain. Currently the policy of the national marrow donor program (nmdp), and its affiliated blood centers which register donors, is to permit only those between the ages of 18 and 60 to register as donors who is healthy enough to that. There a movement to have young people 15-17 years able to register.
Usually 18. Usually you need to be 18 to join one of the registries....But younger individuals can done - ie if one child has a leukemia and a sibling is a match, that sibling at any age can really be a donor.