TL;DR
My one childhood friend asking me for marriage. He is my very good friend. I want to say him 'No' for marriage.
Background
Few months before, I have seen a guy on Facebook in recommended friends' list and recognized him immediately that we were together since 1st to 12th standard. We again became friends. After some days, He asked me for marriage as he is also single. I have not yet answered him anything. But the issue is my expectations about my life partner are different. He does not suit in these expectations. Although he is well educated and well settled but he has a health issue. My parents said "Deny his proposal". I have to listen to my parents and also I myself don't want to marry with him. I would have denied easily his marriage proposal if he would not have been good friend of mine.
The Problem
He is my good friend since childhood. He is very serious and sensitive kind of person. I would like him to remain as a good friend only. I am thinking that he should not get hurt when I will say 'No' to him for marriage.
Question
I don't understand, How to say 'No' to him for marriage so that he will not get hurt?