You're probably not aerobically fit. You can still be in good shape and not be aerobically fit. Your body has to get better at burning energy efficiently. Then you'll be able to run more and more without getting winded. This is definitely something you can drastically improve by gradually increasing the distances you run! When I started running, a quarter mile would get me very much out of breath. Now I can run 10 miles at a good clip and breath comes easily. Just start slow. Get better at running further before you work on running faster. One thing that helps is if you start all your runs at a very, very slow pace, then speed up to your target pace after a mile or so. This will help you warm up and ease into the faster pace. You're less likely to get out of breath this way.
If you think you are aerobically fit, it could be something else. Maybe your running form is inefficient, or maybe your diet is less than great. It could be that the muscles you use for running just aren't in good aerobic shape. That'll get better with practice.
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Your past does not define you; you define your past.