My gut feeling on this is we need more info to make an informed observation on the subject. Some particulars like how long you've been together, do you currently live together and if so, how long, are you sexually active with each other (it can make a huge difference), what support systems do you have in place in the form of family and friends who are supportive of your decisions, what are your plans for the next few years in regards to school and long term goals, and lastly, but possibly the most important, is there anything right now that you would like to change about her in any way (i.e. habits, grooming, looks, sexual tastes, etc).
The reason the last one is so important is that people tend to look past small things like this when getting married because they think they can live with them or worse yet, expect that their partner will change once they're married. The best advice I can give is if you can't live with exactly who they are the day you marry them in every tiny detail of their life, then you need to work on those things before getting married, or don't get married. Don't go into a marriage expecting the person to be different or moldable afterwards. It can happen, but those that expect it to happen are often those that get divorced.
But, something tells me if you're on a car forum asking advice about getting married, it's not a good sign. Take this as advice from someone who married at 22 she was 21, and has experienced a separation including an affair in his marriage. We actually made it through that spot and are happily married and expecting our first baby in a month.
Rick
