am I crazy?!?!?

Am I crazy?!?  I am TTC with my second baby. My current baby is 17 yrs old. My family and friends say I am nuts for trying to have another baby with my son being so old. They say why would you want to start all over. Well, I have always wanted more children but my exhusband did not. When that ended I thought I would never have a chance to. But here I am. I was a teenage mother and I know things will be very different this time around. My nerves are on edge. Am I crazy for starting over. Any advice is welcomed.