According to the note my Mom put on the back of this montage, when she assembled it in a frame years ago:
Top row - 1, 2, 4, 5 and 6 years old
Middle row - 7 thorugh 11 years old
Bottom row - 14 through 18 years old

Most of the old B&W photos have stood up better than the (slightly) more recent color prints.

The bottom right one was taken in 1978. Do the math. :-)