You will certainly improve the health of the recipient and will probably not experience a change in your health after you have recovered from the donation. I do not know if anyone has performed a study that looks at the longevity and health of donors for an extended time. From what I read here, we donors generally go on with our lives with little impact to our health. It has been 5 years for me and I honestly cannot tell the difference unless i measure my creatin or blood pressure. Of course my creatin has degraded as I only have half the filtering capacity. My blood pressure has raised slightly, typically it is now 115/75 where before it was 110/70.
So, total disclosure is that even for very healthy donors, of which I consider myself a member, there is a measurable impact. You must be sure if the impact is acceptable for you. For the recipient, the impact is significant. For my brother it was like we had reversed the aging process, it looked like years of aging had been reversed.
If you read through the boards you will also find that the procedure has risks and it does not always go well. Some have had very tragic results. It is major surgery.
Good luck, and if you continue, know that you will have a positive impact on the person and their family.