For years I either didn't weigh enough or had was within a year of childbirth or a miscarriage or a surgery, so I couldn't give. I would work blood drives as an alternative, they always need volunteers who have no fear of blood and are willing to help! (Most volunteers will never start the IV, or things like that. You participate in patient care, keep an eye on people giving blood, to make sure they're OK and the bag is filling properly, carry the units to the storage refrigerator, hand out cookies and juice, learn to know when someone is going to pass out and get into there with the ice packs and dropping the head of their cot and raising the feet etc.
I just found out I'm anemic (which is a fairly new one for me) so I can't give, still.