I got married at 25 after a 2+ year long engagement and have been (generally) happily married for a little over 4 years now. My husband was 22 when we got married.
But we felt strongly that it was the right decision for us and we have a strong relationship. Marriage is certainly not for everyone, and certainly not if you don't have a strong connection to the person in question. Before I met my husband I wasn't too certain about a for life thing either, because I hadn't met him. When I did, I knew we would be together for a very long time.
Not everyone meets someone like that or feels something like that and sometimes even you do it doesn't work out the way you hope it will. No reason to rush into anything. If your mind changes at some point, awesome. If not, and you are happy, who cares?