Society has conditioned men into believing that marriage is an institution and therefore no sane guy wants to be institutionalized. Their argument is that even prisons are institutions and therefore the reluctance to get married. Having said this most men do get married at some stage in their life and only a minuscule percentage remains unmarried. Here is when they stop fearing marriage.
Loyalty and trust
Many men believe that they will not be able to stick to one woman for long and they will lose the trust of their women after marriage. This self doubt also keeps them away from marriage. Only when they are able to keep their raging hormone levels in check will they be ready to marry and settle down.
Financial stability
The man wants to be the protector and provider and therefore wants financial independence or financial stability before considering marriage. However, when the woman too is gainfully employed this fear goes away.
Ready for parenthood
When a guy is reasonably convinced that he will be a good father his fear of marriage disappears and he begins to look forward to being one. It is up to the woman to convince him of his ability to be a good father.
When the woman gives the guy freedom during the courtship
A guy fears loss of freedom after marriage. When the woman does not appear desperate and clingy during courtship he is convinced that he will be able to do things he likes even after marriage and hence stops fearing marriage.
When he sees his peers and friends happily married
When a man sees that marriage has not dampened the spirit of his friends or peers, his fear of marriage disappears. The woman should make it a point to introduce her man to happily married couples to influence his opinion of marriage.
When it is apparent that there will not be any undue pressure
Most men think that their women will try and change them into something they are not. This fear keeps them from committing to marriage. However, when the woman accepts a man as he is and does not pressurize him to change his ways he does not fear marriage.
When he truly loves his woman
When a man realizes that the woman he is dating or courting is the woman of his dreams he will not think twice about marriage. In such case marriage is the natural progression of things and he does not fear it anymore.