If nothing else I find giving blood gives me a warm fuzzy glow that even the missing blood doesn't stop. Although I do have a period of time that the low blood pressure I tend to get needs close attention.I end up having to watch getting up from couch too quickly or I'll drop like a stone.
Tip for any new donors, drink lots before and after. Being well hydrated I found can speed the donation a lot. I always time my actual donations from after the samples have been taken and the flow opened up. My times range from 15 to 5 minutes. That's, in my mind, down to drinking before. Then after I think you need to make sure you're hydrated something to do with keeping blood pressure up after removal of the blood.
I'm sure others will know if the above tips are valid but they're my experience of what helps and they now make sure you drink a pint before donation. That last bit about blood pressure is important to me as I'm most likely to black.or grey out after blood donations when I've not drunk much.
BTW what is it about reaching a certain old age and not being allowed to give blood? A friend's granddad was one donation away from a big figure when he turned 70 and got a letter saying he was too old to give. Apparently he was as fit as a butcher's dog, walking a lot in the hills over long distances and very active. I've known 67 year olds who've done the Bob Graham round and healthier than I've ever been.