Well I'd believe there is on age limit once you get pass the age of innocence. Although in our country of course outlaw, getting married before 18 seems to be seen as irresponsible and senseless so I guess I'll make the age minimum of 18.
Personally falling in love and getting married are just two different things. The falling in love is the emotional part and the getting married is the business part. Meaning, just like any form of business you have to be smart about it. First, know that you are actually in love with this person because they are stuck there for life... unless you weasel yourself out like most people do in my country haha. Second, make sure you have a steady job and comfortable setup so that you can support a family and not just you. Finally, make sure you have well planned out the future for things such as insurance, payments, and other things.
So old enough to marry is really kinda ambiguous because marriage is a contract and pretty much a business agreement. Don't sign until you are sure you that your signature means something. There is of course the love part but that's not the whole of marriage in our time and that is something that needs to be recognized.