Hi rg,
First of all, it's great you want to donate to your dad!
I donated to Daddy when I was 47, and it was amazing to spend healthy years with him after. His kidney failure was due to medication side effects, so I didn't need to worry about inherited issues. Diabetes does run in my family, though, and I will be careful with my weight and follow-up testing for life. I think all donors (well all people, but especially donors) should watch their weight and diet.
Sherri gave you great things to think about. I totally agree with her. I'll just add that IF another donor appears you could be 'on-call' to be a second donor in the future if needed. If you are 23 I'm guessing your dad is young enough as well to potentially need a second transplant in the future.