What do you tell someone in their 20's who's just lost

"I'm sorry for your loss"

Don't bring up the subject, they usually don't want to talk about it. If the situation calls for it tell him you're sorry for his loss, but don't insist on it.
If they do want to talk about it listen to them. There's not much for you to say, but sometimes just having someone listen to you in your moments of grief may make it feel better.

Other than that it depends. Different things would make different people feel better, that's why we cannot give you advice on what exactly to say or not to say. Since you're not sure yourself I suggest keeping talk about it to a minimum.

>>17585143
It will all be OK, i see ghosts sometimes dw about it.

>>17585143
nothing you say will make them feel any better
just be around
talk about whatever they want to talk about
try to keep doing the things you guys used to do
..
if they are negative, angry or dark - tell other people in their family what is happening and older relatives will talk to them
..
if they are positive and hopeful - support that
..
your job is to keep being a friend

>>17585149
This
And if you are close with this person tell that you will be thre for him/her for whatever he/she needs