IMHO, getting married shouldn't really be about 'making it official' as your love life is personal, but it should be a great celebration about the fact that you are both ready to say 'I want to spend the rest of my life with this person'. As to how long you should wait before getting married, it changes really. I would mark it with events rather than time. Firstly, you have to be friends first, then you have to go out and fall in love, then you have to live together to make sure you are able to be around eachother 24/7 without getting at eachother's throats, then you should wait a while to see if you still have that 'spark' and finally, through all that you should have 2 or more big fights just to see if you can work things out. If all of these are met, then propose, whether this takes 3 months or 3 years, all of these should be met.
Oh, and if it isn't against your religious beliefs, then you should probably throw sexual relations in there too (otherwise the honeymoon could be aw-kward).
Oh, and if it isn't against your religious beliefs, then you should probably throw sexual relations in there too (otherwise the honeymoon could be aw-kward).