Both your age and your genetics play into the chubby cheek equation. Take a look at a two year old type, even if they have a lean body profile they have chubby cheeks; or, look at a Christmas cherub which is the epitomy of a baby/kid/toddler look. Contrast the two year old, chubby cheeked cherub look with any one of a number of older celebrities who have had plastic surgery. As we age, we lose the defintion that generates chubby cheeks: the lines between the nose and cheeks gets deeper while the space between the peaks of our cheeks and lower jaw fills in. Few if any of those 50-80 year old Hollywood types with high cheek bones and well defined jaw lines have come about their looks naturally.
The good news is that "chubby cheeked" folks tend to age more gracefully/in accordance to the ideal than others. It also seems that weight loss, weight gain, and increased fat mass is more readily visible in chubby cheeked folks. Increased muscle mass doesn't seem to be as easily seen in chubby cheeked folks as is reduced fat mass.
...about your apparent, intended goal of going below 12%.....Fat is necessary for the body and all of its functions. We know (proven by research) that it is critical for infants and children upto 2 years of age as their bodies and brains undergo vast and important, physical growth stages. We know a number of things about the importance of fat for brain growth, development, healing, and even just plain functioning. We know that the teen brain undergoes a number of very critical, physical, development stages through the ages of 21 to 23. At 17, I wouldn't recommend dropping your fat mass too much.
We also know that females tend to have a higher fat mass than males. Increasingly, we have been discovering why over the past 40 plus years. It has been whispered from the wings that ballet dancers don't particularly mense for the past 100 plus years. The reason is that their fat mass is not adequate to collect the volumes/amount of hormones required from one hormonal cycle to trigger the next. - The last time I looked, the "female monthly cycle" actually consists of about 5 hormonal cycles which we are typically unaware of that are processing along in the back ground between menses. - As menses were more openly discussed, women started to enter sports at a different level, and more research was done on the female physiology we discovered that the menstrual cycle is negatively affected some where about 15% body fat. Most women have noticeable changes, delays, and missed menstrual cycles when their body fat mass is at 12%; most miss more cycles than not at 10%; and most have no cycle at less than 10% body fat. Certainly this affects fertility and there are indicators that it can cause a number of other problems as well.
Two of the down-stream issues, out side of the reproductive system, linked to low body fat mass are vascular problems and osteoporosis. As low body fat mass hasn't been an issue for me for some time, I haven't followed it to see how strong these links remained and/or what alternative and/or supplementary causes may exist.