Best option to help tone wrinkly skin around belly button?

After having my son, I lost all the baby weight but 9 years later, my abdominal area still isn't the best looking. I am at a stable weight and still working or regularly, but I am wondering if working out is going to give me results I desire. I have wrinkly skin above my belly button and do have stretch marks. While the stretch marks don't look bad, I hate the wrinkly skin. Many of my friends didn't have this issue and their stomachs went back to normal so I'm not sure what to do.

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