I think you may have missed (intentionally or otherwise) the intent of the full question.
Interestingly, currently, there are 2 clusters of shooters by age, 18-21 and then men in their 40s. The current events are skewing towards that younger cluster however, men in their 40s now, would have been raised in that 70s to 80s timeframe you are referring to.
Six of the nine deadliest mass shootings in the United States since 2018 were by people who were 21 or younger, a shift from earlier decades.
www.nytimes.com
Average age of mass shooters overall is 33.2 years. The numbers show it is occurring more. But also, reporting of mass shootings wasn't so stringent in the 70s and 80s, so the numbers likely were under reported.
rockinst.org