Lovelost... it's a gamble no matter what you do. Perhaps later on, age may not matter as much, but right now, she is still undergoing psychological development, mental changes... essentially she is still in the transition from a child to an adult. This means that her perspectives of you and the world around her will change considerably in a relatively short amount of time. Her feelings for you will change too... maybe she'll become more fond of you, or maybe she'll wonder what she saw in you. There is no way to predict the outcome, and nothing you can do to keep this from happening. Either she'll still have feelings for you in a couple of years or she won't.
Also take into consideration your own needs in a relationship. Can she be your intellectual and emotional equal? Can she keep up with what you say and how you feel? or will you have to spend more time trying to explain things pertaining to the relationship to her? A relationship needs to have the workload distributed equally... not just the benefits.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen