How to introduce SO to parents

My SO is 20 years older. My friends all love and accept him for how good he is to me! :) however, my parents don't even know I'm dating someone. His dad and stepmom know and love me. I've met his grandma and a few other family members. I haven't met his mom yet, but she has seen pictures of me and asked about me. He's worried she'll be upset that I'm so young. So, how do I introduce him to my parents without them freaking out that he's going to ruin my life and I'm going to "miss out" on my youth? And how do I prove to his mom that I'm not some little girl who is going to hurt her son and ditch him or use him for his money (or whatever she might think, I'm not even sure lol)...