Sometimes a person may not live as long with one kidney but sometimes people can live a full lifespan with only one kidney.
Also if you donate a kidney it doesn't shorten the donors lifespan either.
If a person who was born with one kidney or had a kidney removed during childhood then the person may eventually lose some kidney function after 25 years or so.
So a person born with one kidney may only live for 50 or 60 years while they may also live out a long life.