I have to admit-I'm jealous

I love my son and would very honestly NEVER change a thing about him but I cant help but experience bouts of jealousy on a regular basis. I see Connor every day and never bat an eye at his delays. They don't seem that significant to me when it's just us.
We had a huge weekend of birthday parties this past weekend and it was like a giant slap in the face. There were tons of children there and I was shocked at how much bigger, older and more independent they were compared to my son. Some where even born on the same day as him.
Connor had a blast as did we but I felt so sad when he wanted so bad to climb on the little play motorcycle and couldn't and then a 16 month old little boy had no problem. Connor doesn't know any different but I do. He gets so mad that he cant do something and I have to sit there and fight back tears.
I never say this out loud to anyone other then my family but-IT'S NOT FAIR.
Connor is making leaps and bounds of progress and I hope with all my soul that someday he will catch up and the struggle will be over.
I don't think of myself as a jealous person but, seeing these other children do things so naturally while my son struggles to do things they did 6 months ago aches me.
I wish there was some way to replace missing chromosomes and genes in humans.