4 is first because it is the furthest layer down.

5 is second because it is the next layer above 4.

6 is third because it is the next layer after 5.

1 is fourth because it is the top layer.

2 is fifth because it is a 

3 is sixth because it cuts through B&A

A is younger than B because it cuts through it

B is older than A because it was cut but A