So you have a child at 15yrs 4mos, the child has your grandchild at 15yrs 4mos, the grand child has your great-grandchild at 15yrs 4mos, and 12 years later you have a 12 year old great grandchild at the age of 58. They don’t waste time. In another 3 yrs 4mos she may be a great-great-grandmother at age 61.
oops. she is 70 now. so that’s all having kids at 19.