As we are using ONE teacher as empirical evidence, I would just add that the point of maintaining discipline is to aid learning. The evidence provided suggests that whilst said teacher did indeed scare the excrement out of you, there is little evidence of any learning.
This is the crux of the issue. It is not about teachers retiring now, but about those who are due to retire in 10 years plus time. 67 seems a ripe old age to be controlling a class of unruly teenagers. Some will relish it, but others may really struggle.