Violent crime in 1992 was about 800% higher than in the 1950's at least in America.
It's come down a little, but crime is still about 600% greater than in the 1950's.
http://www.pewresearch.org/fact-tank/2016/04/25/millennials-...
Note that the article talks about the number of living Boomers and Millenials surpassing them. I'm not making that point. The max number of Boomers was about 79 million. 75 million Millenials is quite comparable to that.
So is the fact that the item you're comparing today's still living, old Boomers to a by definition much younger Millennial population. There were once quite a few more Boombers, and circling back to my entire point, young Boomers of the criminal producing age.
I also disagree that a ~5% difference would be likely to drive significant differences in crime rates.
Later: Yes, that Millenials are a smaller percentage of the population would complicate the comparison.
You're clamoring for a soap bubble that didn't withstand a tiny pinprick.