Dear MG,
Hi. Welcome. I donated a kidney 14 years ago, and am doing fine now at age 70, still doing distance running.
There have not been many long-term follow-up studies of living donors in the U.S. Most hospitals just barely do some check-ups until 2 years after donation, if that. In Europe there have been some (few) really long-term studies of living kidney donors, comparing them not to the general population, but rather to persons of their own age who had passed similar health checks but had not donated. Crunching the numbers did show that kidney donors have a higher rate of kidney and heart problems later in life. (I don't have the exact numbers, nor the study itself. Donors' results were poorer than non-donors to a degree that was noticeable but not terribly worse.) When they further crunched the numbers they found that those who had donated to a blood relative had worse results than those who donated to a non-blood relative or friend or stranger. So the suspicion is that there may be unknown factors in the genes shared by blood relatives that MIGHT produce a greater tendency toward kidney disease or its causes.
So, there is some risk involved, and each potential donor should take that into consideration.
There are 2 sites: Livingdonor101, and: Living Donors Are People Too that give a LOT of emphasis to every possible risk.
These days a lot more people check in at the FaceBook page of Living Donors On Line rather than here, so you might want to post your message there as well, as you will get more responses and sharing there. You can also learn a lot by reading past postings at this site.
I hope some of this info helps. I would gladly donate again if I could, but I now know more about the possible risks than I did at the time of my donation.
best wishes,
Fr. Pat