I think we need to remember he made that statement back in 2009 during a Football life. It was the low point of the 20 year run, most of the leaders from the first part were gone and it was not known i do not think how long the run would last at that point.
So he might of been thinking he might have more years like 2009, which would make anyone not want to coach past 70.
Now that things are running smoothly, the record is in reach, even if TB12 retires, BB can smell it and wants to go for it. And you can not blame the man.