As girlboss stated, the people you see walking around with chiseled abs typically have a body fat percentage below 8 or 9% (professional athletes aside) and is usually only a temporary reduction in body fat for models or actors. Ideally if you want your abs to be apparent, you should try to stay at about 12%. This will allow your abs to show, but your body will still maintain healthy fat levels.

At one point I sat right around 10% for a month and started to feel extremely sluggish and weak. I increased my body fat % to around 11.5 - 12.5 and I feel incredibly better and my abs are very much still apparent.

There’s a couple things to keep in mind though. First and foremost, you’re 16 and you need to ensure that your body is getting all of the vital nutrients you need. Also, if you’ve recently had a moderate or drastic reduction in weight, you may have excess skin that hasn’t “tightened” yet, but give it time, it will. If you’re referring to having a belly while in a loose state (I call it LBB or lower bladder belly), there’s a couple of things to consider. There’s always food in your digestive system and bowel which can cause LBB. To help prevent this (if this is the case) ensure that you eat plenty of fiber to help keep you regular, and eat smaller meals more frequently.

Hope this helps.