I went to my orthodontist today and got x-rays done.?

After i got the X- rays done he began to make 4 circles on the paper in the back of my mouth. He began to tell me that i didn't have Wisdom teeth. Is this Possible? What makes this possible? Is it common? Please help me out. I am curious as to why i don't have them but both of my parents do. (By the way I just turned 14)