You all know what immortality is,yeah i know.
Who doesn't know,here's it:
You don't die when your immortal.Even if Goku becomes SSJ4,
Loads a Kamehameha on you,Trunks slices you,Piccolo 'laserbeams' 
you and Gohan loads a Masenka on you,well,your probrarly think that's not
healthy.You think,i migth go to the hospital for a few days.
Well,if you are imortal you can consider about that.
If you aren't imortal,well,ehmm...then...ehmm...htink about it
yourself,or lett your mammy kiss u..LoL...
Here's a list off people who are immortal,and people who wanted immortality
such like Frieza,but didn't get it.::.

Master Roshi:
He didn't wished for immortality though.
He has dronk a bottle with stuff in it that gives you
immortality.That's one reason why he's looking so old.
In the beginning of dbz,He's 579 years old.

Turtle:
I'm not sure if Turtle has go immortality.
But that again,did you ever saw a Turtle who's 1000 years old?I didn't.Out.LoL.

Garlic Jr.:
He wished for immortality though.We never saw this in any saga in DBZ,but
this was all played in Movie #1:The Deadzone.
Maybe i'll make a movie about this,and post it.But i've saw it on
planetnamek.com/Multimedia/Movie Clips/DVD/Movie 1/Garlicjrgetsimmortality.blablabla..Out.

Frieza:
After Frieza heard about the Dragonballs,he wanted to wish immortality.
VBut luckily Gohan,Krillin,Vegeta & Goku fougth Frieza so it could not happen.

King Yema:
Just like Turtle,i'm not sure about this,but i'm about considered that
he's very old,and i thougth it was 1000 years ago when King Yema ran the Snakeway.
[This was when Goku had to go to King Kai].

King Kai:
Just like King Yema....

Mr. Popo:
Yeah,even like many others i'm not sure,but he served about
all the Earth Guardians.He also knew loads of guys when he went with Kami
to put the 'anitdote' 4 the Black Water Mist in a put.

Dr. Gero
I knew he told to #17 and #18 when he just let them go he said that he had eternal
life.I believe him,becuase he stilled lived when #17 kicked his head of.LoL....