How can she let him know that her answer is "no"?

ok so my best friend likes this guy and he likes her back but she doesnt want to go out with him because of age difference and other reasons and they are really good friends but he doesnt understand that she cant go out with him and no matter what she...

tells him he wont get it through his head. she is not the kind of of person that can be too mean and stop talking to him completely especially because he has a depression problem and she is afraid of what he will do.
what advise can i give her?

FUCCC*K this 1 is hard!! idk i mean he's got depression problems and if she say's that she jus can't who knows what will happen!! why dnt you go with her to tell him at the same time so yall wnt get hurt!! just in case!! or make some1 mean tell him so he'll get it through his head and make that guy tell him that you sent him so he wnt be mad at her!! lol horriable advice nvermind dnt listen 2 me...

If your so afraid of him, why are you his friend? If he doesnt get it through his head, she needs to start ignoring him here and there, not just completely shut him out. He will eventually get the point. Maybe a friend needs to also step in, and tell him if hes not getting what your friend is telling him!!

Perhaps she should tell him straight, i dont wan to go out with you so get over it i just want to be freinds thats all maybe he hasn't got any depression problems atall maybee he's just saying that to make her feel guilty and sorry for him